Actually timedelta is the reason it can skip.
If your not terribly worried about v-sync, you can set it to unlimited. Otherwise all you can do is make sure the ball, and walls are not set to point. Then increase the size of the ball, and the walls.
One thing you might try is scaling the objects bigger, and scaling the view so they then look smaller....not sure if that will really help tho.
Also the hotspot on the ball is a little off. That with rotation could be making things worse.