You've gotten great advice above from Deborah and I think you're stressing too much over this. Your snake will not be massively over-fed if you feed him
2 of the size you have, & as long as it's not something you keep on doing. It also won't hurt him a bit to eat just ONE item...it's usually better to underfeed
just a bit than to over-feed. The issues with feeding 2 at a time are that (1) some snakes will only accept one prey item at a time no matter what, and (2) of
those that accept both, you run the risk of overwhelming their digestion and causing them to regurgitate...a very real set-back that can be harmful. So between
the 2 options, I'd personally just feed one under-sized item for now & not lose any sleep over it. Snakes have evolved eating far less than most of our pets
get (even with more activity) and a little hunger won't hurt. And remember that in the wild, their food is NOT all the same size, nor at the same frequency.