I wouldn't worry, in my experience, doctors only do measuring do they can bully and push into a section. Most women can give birth safely to a 10 and 11lb babies.
I've not had a single ultrasound myself and my midwife says baby feels just fine.
When my mom had my sister they told her she was extremely small and her legs were to short. Mom is 5'8 dad is 6'1. When she was born they found that she was just curled into a tight ball and within the first 2 months she sprouted. Now she's 7 and and most as tall as me at 20
I've had four children. They weighed 8/8, 6/15, 6/2, and 7/4. If your doctor isn't woried, I wouldn't worry.