I found out the hard way that it is better to ask for advice on how to do the repair before you start on it.
Personally, I would not have used epoxy, I would have used Titebond III Ultimate Wood Glue. The main problem I have with epoxy is that you can never hide the glue seam...it always shows and looks unnatural.
Are you planning to fire the gun at all, or use it at re-enactments? If yes, I would not have confidence in the durability of an "epoxy only" repair.
For firing/handling, I would recommend that you reinforce the repair. I would drill two very small diameter holes through the sliver and forestock and then glue in dowels that would physically connect both stock pieces. The first hole, would be diagonally downward from the back of the forestock sliver (the part that butts up against the metal receiver) into the forestock, and because this is "hidden" when the gun is assembled, I might drill a bigger hole and used a bigger dowel than I would for the second hole. The second hole I would drill upward from the bottom of the forestock into the sliver, at a point about 2/3 of the way forward (toward the muzzle). This would be a thin diameter hole (less than 1/8, depends on how thin a dowel you can obtain). Unless the dowel was made of the same wood as the stock, I would set the dowel so that after it was fully inserted it would lie about 1/16 inch below the stock surface, and then fill the little hole with a mixture of glue and sawdust from the original stock (ideally stained to the colour of the original stock), to help hide the dowel. If you couldn't get a nice looking "filled hole", you could fill it with various furniture-crack repair options (like wood-stain coloured wax crayons), or even use a small rock to create an indent there to make it look like the stock got dinged by a rock during firing/combat.
Remember, that you don't want to drill completely through the two pieces of wood you are joining...you only need to drill partway into the second piece (halfway usually good enough, but it depends on how thin the wood is, the size and diameter of the dowel, etc). You also need to be absolutely sure of your drilling angle, so that you don't pierce the stock surface unexpectedly. Putting a mark on your drill bit will help ensure you drill no further than the mark that you carefully measured.
When gluing in the dowel, fill the hole with glue, and coat your dowel with glue, then insert, tapping it in with a hammer if the glue makes it a tighter fit (however, your hole should be drilled slightly larger than the dowel so that you can insert it all the way without it getting stuck; do a "dry" test fit before you add the glue to make sure it goes in all the way, and cut the dowel to the appropriate length).
This is all "in theory", I might have altered my approach with the actual stock pieces in hand, but your pictures give a pretty clear idea of the task.
Alcohol will indeed help get rid of the epoxy residue that you have, but it will also weaken the glue that holds the stock together, so be careful when you use the alcohol near the actual glued joint. Perhaps others have some better suggestions for epoxy removal.
Hopefully, the end result is very satisfying! Best of luck, and please continue to update us on your restoration project.