For now this is an easy fix sweetie, just feed two or more mice.
Most of us run in to this problem at one time or another. The easiest solution is just to feed multiple prey items for a while. While not ideal, most of us do it at one time or another. I have a few dedicated mousers. While a couple only eat two or three mice, I have one male who will happily eat four or five if I let him. He's 2500 grams, and should be eating rats, but he wants no part of them. So mice are what he gets.
Since ball pythons grow at different rates, I wouldn't worry too much about him. As long as he eats regularly, and you aren't trying to feed him pinky's, he'll be fine. But do give it a try. Offer him two mice next feeding. Let him eat one, get his jaws readjusted, then offer him another and see what he does. Of he takes them both, next time do it again.
Gale