20 weeks and 90th percentile??

Hi! I just had my 20 week anatomy scan and the doctor said my baby is at the 90th percentile in terms of size. Yikes! I’m a small person and not showing much and freaked about having to push out a huge baby. She also said that the baby is measuring more like 21 weeks so maybe the 90th percentile thing is just saying that I’m ahead of schedule for my due date? Anyone had something similar?