The first thing you need to do is slow down.
I know you are excited to make a knife, but slowing down and thinking things through before starting is important. If you haven't, you should read the stickys. After drilling the tang hole, it would have been a good idea to reduce the amount of wood on the block at least 90% before epoxying it up. Checking the alignment before the epoxy set would have helped, too. Right now, you are stuck with what you have done, unless you want to take the handle off and start over again.
Normally, you would have shaped the handle part-way and made at least the front part the size you wanted before gluing it on. As it is, you can't really work up at the guard very well without marring the guard up badly. You may have to accept that.
To remove the handle you can either pound it with a hammer against an anvil or a large brick/rock and break the handle off, or heat the handle with a heat gun or propane torch until the epoxy breaks down at about 200F. The torch is how most folks do it. Just keep the blade out of the flames. When the epoxy starts to break down, you will be able to tap that nail out and shortly later will be able to pull the handle off with gloved hands. Once off, clean up the excess epoxy, plan the handle and make it, then glue it on after most all the shaping is done. You should do all that outside, as it smells and is messy.
As for finishing it as-is:
When your knife is finished, the pin will be higher/lower on the sides, but that is just cosmetic.
You would do yourself a favor if you can find someone with a belt sander to at least grind away most of the excess wood, because what you need to do now is start removing about half of that block. It would work best if you had some way of holding the blade while working on the handle ( vise, clamp to a board or table, etc.)
Start by taping the blade up with several layers of masking tape ( the blue painters tape is the best for this). The tape will help protect the blade from getting scratched up.
Use files, rasps, and sandpaper to start shaping the handle. As you remove wood, check the shape from the end to assure you are making it line up with the blade. You can use a wood carving knife or pocket knife to help shape the handle at the guard.
Once shaped and aligned as you wish, sand it to finer grits up to at least at 400 grit.
Next knife, make a full plan and sketch before doing anything.
BTW, did the "kid" that make the blade for you heat treat it for you?