Good effort, but buggy
Jezzball is a fun game, and I'm actually surprised no one's made a flash version of it up to this point. Your game looks and plays well, and if it weren't for some major bugs, I'd give you a 10. The bugs I noticed are:
1. If 2 balls bounce off each other near a wall, one ball goes THROUGH the wall, often getting dumped somewhere random.
2. Occasionally, you'll trap a ball in a box, but the other half of the area doesn't fill. This one's minor, as you can draw a line anywhere in the empty box, and it will then fill all of it.
3. If a ball MAJORLY glitches due to #1, your percent counter FREEZES. No matter how many squares you fill, the percent will not go up, you cannot complete the level, and you automatically lose the game.