Baby measuring small?

I had my first ultrasound today, my actual doctor did it though instead of the ultrasound tech. She said everything looked great and baby’s heart rate was 134. She did say that she’s not great with measurements, so she sent out an order for me to go get another ultrasound because she said baby is measuring a little small. I’m 7 weeks 4 days but baby is measuring 6 weeks 5 days. She thinks it’s her error, but if it’s not should I be concerned?