20 week scan.

We had our Anatomy scan today at 20+2. We just had the ultrasound, no dr appointment until next week to go over findings. I’m a little worried that her head circumference is only measuring 19wks, along with her abdomen. Her legs and arms are measuring 21weeks. Is this a problem? I asked questions during the scan, but the tech said shes not aloud to give me definite answers(understandable). Has anyone else had measurements that are behind and ahead? Is this normal?