Was my 18 week ultrasound normal?

I got the ultrasound report from my 18 week ultrasound and it said the baby was in the 37th percentile and that I had marginal Placenta. I've heard the marginal placenta is normal and goes away later in pregnancy. My doc didn't say anything to me about either. Will I have a small baby? Anyone have any similar cirstances? And how did it turn out?