I've heard some people recommend feeding between 1- 1.5 times the snake's girth. That said, I imagine "pet" rats are probably bigger than pups, which is what my ball ate at 6 weeks.
Now that he's eaten, all you can do is take good care of him. Make sure the warm side is warm enough to help him digest, and give him an extra day or two before disturbing him. I'd wait a good 10 days before the next feeding, won't hurt. I fed a big meal once and it was never regurged even though the snake still had a visible lump 2 days later.
Good luck! Let us know if it comes back up...