This is the best textbook for learning discrete math: https://www.amazon.com/dp/B00B6FAZ2Q/ref=dp-kindle-redirect?_encoding=UTF8&btkr=1
If linear algebra didn't make you comfortable with proofs then also this: https://www.amazon.com/How-Prove-Structured-Approach-2nd/dp/0521675995
Between those two you will be good. Unfortunately halfway through the semester is tough. If you are below a C I would drop it and retake it with better prep next time.
On the plus side, if this puts you behind consider taking on a Math or Statistics minor with the slack time. That can put you in the running for better grad school or job opportunities later on.
For Discrete Math, I would recommend Susan Epp's text. For the non-technical skills... you're on your own. :)
First, I'm not connected with JMonkeyEngine at all. Just a coder who stumbled upon it and is pretty enthusiastic about the possibilities it opens up.
> I would like to actually do some coding, and not just leave it all up to a third party game creator.
JMonkeyEngine is not GameMaker Pro. It's a genuine framework requiring genuine code. It just tends to abstract away some of the hairier stuff. But you do need to know details like vector math and quaternions and other stuff from this book to use it effectively.
That said, it is intended for 3d games, so it might not be best for you. In spite of what others have said, however, creation of 3d games are not out of reach for a hobbyist -- there's a fair amount of free 3d assets out there, as long as you're not too particular about how your game looks.