growth scan at 33 weeks

I had my prenatal appointment today and my doctor wants me to get a growth scan this Friday as my baby girl is measuring on the small side, I'm pretty nervous! At first she was in the 63% percentile but My doctor said she just wants to make sure that she's still growing and that it could just be the position she's in, however I was told told that if she is in fact measuring small that they will do one more ultrasound at 34.5 weeks and if she still hasn't gained weight by than they want to get her out by 36 weeks which by than she will be full term.. I'm pretty nervous as this is three weeks away! Anyone else in this situation that can give me a piece of mind?..