Doctor appointment: small baby?

Nancy • My daughter Ava Grace is my world! 05.04.16 Expecting March 2019
I had my doctors appointment today and they said based on my belly measurements Ava is still measuring small. There doing an ultrasound tomorrow to make sure she's on track. She is most likely going to be a 5 pound baby, but will know more tomorrow after ultrasound.  Anybody else dealt with this before? I'm kinda nervous!