How do you "accidentally" add fish ? LOL. You knew you were adding them when you put them in because you had already bought them at the LFS. If you are worried now, why were you not worried when you bought them ? I don't get it.
Anyway, you have them now, so just keep on top of monitoring your water conditions and be prepared to to some big water changes if you get a spike. Alternatively take half of them back to the LFS and tell them your tank cannot handle this many fish at once, and they should have known that. Some LFS's suck. BIG TIME !
Good luck. You could go out and buy some zeolite tomorrow and put it in your filter and it will handle any excess ammonia hopefully.