It's okay. I have snakes that routinely swallow live rat pups because they're too excited to bother killing them first. My hognose regularly has a squirming lump in his middle. As near as I can tell, this is harmless. Okay, I don't like it either, but it doesn't appear to do any harm.
You're probably right -- it probably didn't know to constrict. My corns didn't start constricting until they were older. They, like yours, had always been fed thawed prey.
If you can, you might want to just offer frozen/thawed food to your baby. You have a good thing going with a snake that will take pre-killed food, and there's no reason to keep it on live food. It isn't any 'better' for them, and the convenience of feeding thawed is worth it a million times over. You'll be really grateful when it starts to eat full-grown mice (sooner than you think) that you don't have to kill!
I think it's really great that you're that concerned (even if you don't have to be
). If you have any other questions, just let us know. We're always around to help.
Does the snake have a name, by the way?
--Naamah