Let's see what I can say about this...
The boundaries for the ships movement should be the same as the screens dimensions sideways.
It's slightly weird that incoming asteroids are faster than enemy bullets.
I like how you made it auto-fire so that I don't need to hold or spam a key for no reason.
Speaking of that, there isn't really a need for holding down the mouse button for movement.
Good job for your first game being practically bug-free.