Love the music and art :) REALLY fun idea, and the interpretation of the theme is very unique and I think one of the best examples of creative uses for the limitation, with the most distinct double-actions from a single button. Kind of an interesting way to implement braking for turns.
I think it was sometimes hard to feel the immediate effect of turning since the inertia was so high for turning and it would take several seconds before the 8-directional sprite changed. Some way to indicate your arrow key is working immediately would be helpful for the player feedback. You also weren't kidding when you said "Impossible" difficulty! They smoked me in that race!!
Really good job! That was a lot of fun