This isn't a program where you edit the shapes like Blender or SketchUp, this is an astronomy and gravity program, you simulate gravity, though you can also simulate models, but you can't change the shapes of them(other than the astronomical bodies, by changing their mass), that's Dan Dixon's job to change.
Yet you can't control the shapes of the balls like you would on modeling programs, they come out the way they come, and they don't get rounder by adding mass like astronomical bodies would.
Also, like I said, the Pool Balls are low poly, which is why they're not round enough.
Also, here's another screenshot, this time of a cue ball, the white might make it easier for you to see the flaws.