They grow slowly when they're on pinkies so it takes a while before they size up. Figure feeding 2 pinkies weekly for probably 2 months before you go to fuzzy mice
(aka crews), & it will take probably 2 months of eating fuzzies before they would take anything more, but just double up on fuzzies for a while like you do with pinks,
before going to hoppers. It's hard for us to answer this because we aren't seeing your snake...the actual size. You want to feed a f/t rodent that is NOT wider than
the widest (un-fed) part of your snake's body, no matter what size they're eating. If you have some pinks (or whatever) left over when they are big enough to take
larger, just feed them off (multiples per feeding). Adult corn snakes eat adult mice...but not jumbo mice (aka old breeder mice)...those are too big & too fatty. OK?
And as your corn snake grows up some & eats larger prey (hoppers & up) you want to lengthen the time between meals. Hatchlings eat weekly, but
once on hoppers, gradually extend the time between meals (larger prey takes longer to digest & is more filling). Adult corns eat about every 2 weeks, or
every 10 days in summer or if breeding (at the most).