Baby measuring small. Worry?

So I had my anatomy scan today. I’m 21 weeks today based off date of conception and LMP..but my baby was measuring 19w6d according to her measurements. I was told I had to get a call from my Ob and when I did she said I’d be seeing a high risk doctor instead of her for my next appt. ugh any other moms have experience with this? Not sure if I’m worrying for nothing as I was told ‘all your questions will be answered with the high risk doctor Monday’ when I asked anything.