I'm guessing this is too late to help, but next time try adjusting your oven temp (reducing slightly). It really depends on how far too small the pan was. For example, if you used an 8" round instead of a 9" round, you could probably get away with just adjusting the oven time (not temp), allowing to cook a little longer and doing the toothpick test to know when done. If, however, you used a 6" pan instead of a 9", now you should probably reduce the oven temp slightly (say from 350 to 325) AND expect a longer baking time.

How'd it work out?