Pregnancy questions

I am a ftm and only 19 I was just at the doctor for a checkup for my 30 weeks and they said they think my baby is too small and I will have to get another ultrasound done at the high risk center to see if my baby is getting enough nutrients through the placenta and they also said I have "pools" in my placenta but that I shouldn't really worry about them because a lot of people get them. Is there anyone else who has had this problem? If so were you able to have about healthy baby? I about very worried and waiting on my ultrasound from high risk in a couple of days.