Head measuring smaller than belly?

I just went in for my cervix check and ultrasound to measure my baby girl. I’m 36 weeks + 4 days and she is measuring 6 pounds 8oz. They mentioned once before her head is measuring a week and a half smaller than her the rest of her. They told me today still the same and her belly is definitely bigger than her head. They keep seeming like it’s normal and almost chuckle at it when they say it but I’m concerned! I know with my son his head was huge and way bigger than the rest of him. My daughter is the opposite. Has anyone else gone through this and everything be ok?