Nice to see a lowres build of this concept.
One thing I noticed is when holding down the jump button, you will repeatedly jump in the air. I don't know if this is intentional or not. If not, one way to get around this would be to have a variable track that you are in the middle of a jump when holding down the button and if the game confirms your jump is still active (because you held down the key), it will not allow you to jump again. Only problem I see with this is you have multiple keys for jumping, but since you appear to be a skilled coder, you would probably find a way around it.