Really nice idea and execution! The gameplay mechanics are incredible. Everything fits well together with the visuals and the audio.
I wasn't able to achieve the goal(actually I was far from it) because I am being outran by the enemy the entire time. However, my friend tried this, and somehow managed to get to 100% easily!
One suggestion is to make the enemies spawn at random places when you press space, giving a bit of variation to spawning.
Great job!