I recently took my boards (though not for nursing) and I looked over a couple of main points the night before and got a good night sleep. I was stressing pretty badly pre-exam but stress really doesn't do you any good (as you already know). I'm sure you will do fine though
BTW The NICU is my favorite unit to do work in and I think it's wonderful that you will be working there. It takes a very special person (and a great nurse) to work with those tiny babies.
Good luck! LIOB