You have to manage your breeding.

Look at the "sticky" section for a breeding plan so you get roughly the number of rats you need each week (you will have about a 2 week window before the rats get too big)
Find a petstore that will take any extras (or other snake breeders)
Feed off the males first (so any females that get to big can be used as breeders)
Adpot retired breeders to pet stores or via Craigslist as pets. (until you RTB is big enough).

Just a few ideas hope they help.