9th Percentile HELP PLEASE

I'm 32 weeks tomorrow and had a growth scan today. His head was measuring at 30 weeks and 2 days, his arms and legs were measuring around the 28 week mark. He weighs a kilo and a half. The ultrasound tech said everything looked normal but then I was sent up to the assessment unit. They said my baby is in the 9th percentile and if I feel any movement decreases to go in straight away. This made me worried, Im a FTM so now I'm stressing. Dad and I are both short and small. But I don't understand why the ultrasound tech said everything looked okay except for his arms and legs if it wasn't okay?

Did you have a 9th percentile baby? How was your baby upon birth? Need something to ease my mind.