First piece of advice is SLOW DOWN. Think things through, an if you have a problem, figure out the whole process to fix it before you rush ahead and do something hat isn't right. If you ask a question here, wait till you have the answers before going ahead with something else.
Your re-grind will be hard to put a handle on and have it pointing the right direction.
You want to drill a hole in the antler that will fit the tang, and then use epoxy to set the tang in the hole.
You might want to go back to your forge and hammer that tang so it goes more downward. Do it at full forging heat so the metal bends down easily.
Now, about your blade shape:
That is what we call a "banana blade". It curves up as you move the steel at the edge. The way you avoid this and get a straight blade is by forging the bar down in a reverse banana before you start forging the bevels. If the blade starts rising too much, forge if back down to a slight downward bend again. When done with the bevels, the blade should be straight.