Regarding the wing joint,

I've got a question for you...

Looking at your pictures, it looks like you sanded a round end on the sheeting. So the question I have, are the gaps thru-and-thru, or is it just a surface gap? If it's all the way through the wing, or deep into it, then there are structural issues. If it's only surface because you rounded the ends of the sheeting, then it's not so bad.

If you want to try to fix the wing, you can try to remove a couple pieces of sheeting, say the pieces behind the spar, and try to add some reinforcements or fix the problem......

WAIT A second... you got a heat gun? Won't epoxy melt with heat? Give this a try. Mix up some epoxy and glue a couple scrap pieces together, wait overnight. Tomorrow, fire up the heat gun and try to heat the epoxy and separate the pieces. If that works, you should be able to do the same with your wing halves.... Then while the epoxy is still warm, scrape away all you can... If this works, you can fix all you can, and re-epoxy later.

Again, this is your plane, and your build.. Do what you want, or not....

I can't stress this enough... it's your plane. Not mine... so do what you think is best. If it flys, it flys. If it fails it fails. You pick up the pieces, and go from there...