Nah, that pretty girl is what a ball is supposed to look like. People see so many skinny, neglected balls and pet shop "maintenance fed" ball pythons, they forget ball pythons are supposed to be round and plump.
I will tell you how you know if a ball is really fat. If you can see patches of light skin in between the scales when the snake is relaxed, then it's fat. If not, then it's healthy.
Also, if your ball python is angular and not round, then it's too thin.
Gale