Looks pretty good!
For the slot gap problem, make a front bolster next time.
It can be a thin piece of brass or nickel, or a piece of wood. Most Japanese kitchen knife handles have a slice of dark wood ( or buffalo horn) as the bolster. African Blackwood is my WOC ( wood of choice) for this. While it can be an inch thick, thinner works just as well.
Cut rectangular 1/4" thick slices (about 1X1.25" is good for most knives) , with the grain, and sand them flat and smooth on both sides with 120 grit( it is simplest to cut a bunch and have them on hand for handle projects). Sand one side to the final grit and polish. Mark and cut the slot out with a jewelers saw. Work it on and off the tang until it is a snug fit where you want it to be on the blade. Make sure it is sitting at 90° to the tang and not cocked. I like having two small shoulders on the tang for the bolster to rest on, but it can just be a force fit against the taper of the tang.
Make the hole in the main handle so the handle slides on the tang and seats against the bolster comfortably. It should not be a tight fit, but it shouldn't be sloppy, ether. Make sure the end fits flush against the bolster.
At glue-up for the handle, mix the slow cure epoxy and tint it black ( 24 hour cure is best). Put a tiny bit on the tang about 1" back from where the bolster will sit and slide the bolster on. It will push the epoxy in front of it and also seal the bolster seam. Wipe off any excess with denatured alcohol at the front and check for a good seal.
Fill the hole in the handle with sufficient resin, and slowly slide the tang in. Run it up to the bolster, wipe off the squeeze-out with denatured alcohol and check the fit. If all looks good, clamp in a handle jig. Wipe off again and double check alignment of the bolster and handle as well as that the blade is straight in the handle. Let cure for 24 hours.
After curing the epoxy for at least 24 hours, grind the bolster flush with the handle and finish shaping the handle.
Note:
You probably have read to use acetone for cleaning up epoxy. I read that, used it, and recommended it for years. Some more recent discussion with epoxy manufacturers has brought to light that denatured alcohol is far better for removing uncured epoxy. It is also safer to breathe, easier on the skin, and cheaper. Cured epoxy can be rubbed away with acetone if you miss some.
TIP 1:
If using a thicker bolster block, say 1", drill/mill/rout the back side out to within 1/4" of the front. Use a 3/16" or 1/4" bit/burr. This gives room for the tang to be fitted snugly in the last 1/4" as above. It will make fit-up of the handle to the bolster easier.
TIP 2:
Making a handle jig is almost essential if you want good tight handle assembly. It is really simple, and can be made for a few dollars. It consists of three parts:
1) A support for the blade tip, guard, or front of the handle ( depending on knife type).
2) The adjustable rails.
3) The pressure block for the butt.
Start with the main support block. It will usually be one of two types. A block with a small hole drilled in it, or a block with a slot in it. You want to make at least one of each, and may end up with several sizes of the slotted blocks. I suggest cutting out eight blocks and having the extras on hand for custom blocks when needed (two will be for the butt blocks).
Cut 6" long blocks from 1X3"poplar or pine. Mark the centerline on each block. Using an "H" or .266" bit, drill all the blocks with three holes - 1" in from each end, and one dead center. Slot one block in the center with a 1/4" wide slot about 1.5" long. The slot should be perpendicular to the centerline you drew, and the lines should bisect each other. This should allow use on most blades to go through the slot. You can slot the extra blocks as needed for specific knives that you make often for a closer fit.
The two butt blocks are: one left as-is with the center hole, and one with a 2"X2" piece of rubber glued in the center. Any piece of rubber will work, but 1/2-3/4" thick dense foam like is used on a Kydex press is the perfect type. Leather will work, too. What you are making is a padded non slip surface for the handle butt. The one with the plain hole will be used in making knives with a through tang and some other knives with a centered handle or pommel. Enlarge or shape the hole as needed to fit the pommel end, or tang. Butt blocks can have different shapes or pads on both sides and can be flipped over to use the best one.
The rails are two pieces of 1/4" thread-all rod. A 36" piece cut in half gives a jig that works for most knives.
While 1/4" wing nuts will work, two 14-20 hand wheels/knob from True Value, Woodcraft, Rockler, etc. will work much better.
At the support block end, attach the block with a 1/4-20 nut and fender washer on each side. Snug them down and that end is done.
Slip on an end block and slide it down. Put on two fender washers and then the hand wheels. The jig is ready to use.
To use the jig - Caution - always do a dry-fit to check that everything is right -
Place knife tip in the support block hole, or place blade in slot, depending on the knife and handle type. If needed, make shim blocks to adjust for angled guards or special blades. Slide the butt block against the handle butt and run the wheels down to it. The block with the rubber pad is the most adjustable, so it gets the most use. Move the handle left/right/up/down as needed until the blade/handle/guard/pommel/etc. all are aligned. If it won't match up, take off and check that all surfaces fit properly. In the dry fit you will find the cracks and misalignments that seem to be missed when covered with resin, and show up badly after all is cleaned up and sanded. Remove the handle, put epoxy in and on all the appropriate parts, and re-assemble as before. Wipe off excess resin and carefully tighten the wheels. It should only be snug, not a forced fit. Wipe off again, check, rotate and look at it from every direction, set it down, and check again in 10 minutes. Repeat as needed until it is dead right...then set aside to cute in an upright position. I like to clamp he blade or jig in a padded vise so I can stand back and look at the handle and blade alignment from all sides.
I agree with Lloyd, I think you could still add some dyed, dark brown or black epoxy to fill that gap so it looks better and so nothing can get caught in there.
