Robotron Like Game (need some help)

[zero00]

I've been playing more arcade games and I came across a game called "Robotron: 2084", a twin-stick shooter. I wonder if I could make something like that.
I modified my one of my Sky Warrior worlds. The ship can now fire in eight directions by using the WASD keys!
There are also "power ups" that increase your firepower (mostly functional) and shields (not very functional) and add to your score.

Problem though, if you press WASD keys rapidly, the bullets gradually don't come back, and eventually you can't fire. I'm not quite sure what the problem is. If anyone can help, that would be great!

(I think the issue may be in the code that turns the bullets around)