I've changed the blocks multiple times, but every time the points show up negative.
It's a game where you have to guess whether the next card is a higher number or a lower number.
Instead of two if..then Blocks in your LOGIC use a single if..then else Block in both the Lower_Button and Higher_Button.Click event handlers. Not sure you are using the not correctly either.
Experiment with your logic Blocks. There may be other issues. It is difficult to determine errors by inspection and without DoIt debugging. 
You have to experiment because you have the aia.
What would a sample game sequence look like?
You would get on the game and there are two buttons and a card image showing. You have to guess whether the next card is higher or lower than the previous card. If you guess right then you get a point, and wrong then you lose a point.
I'm trying what SteveJG suggested to fix the points problem right now.
I don't see the sense in those two global lists, one of "High cards", and one of "Low cards".
What if two consecutive card choices are from the High Cards list? Which would be higher than the other?
Which card is higher, the 7 of Clubs, or the 7 of Spaces? How do you want to handle that?