Couple of recommendations, in no particular order:

1. Keep the ball moving even after you die. Instead of pressing start, the user will just click when the ball is back inside the colored area. 2. You can click anywhere to restart, but you have to click the play button to restart. You should allow the user to just click anywhere to restart. 3. When you fail, show where the ball was. 4. As for collision detection, I think you should err on being lenient and count success if the bounds of the circle overlap, rather than the center or entirely. I think this is also due to the rounded linecaps for the arc potentially not counting as part of the valid area. 5. Show where the next arc will be. This is more of a game design thing. If you do this, quick fade out of the old and fade in on the new would look nice.

I understand that this was probably a small little one off project, and that there's always more you can iterate on, so I just want to say nice job in putting out a fun little time waster!