Baby measuring three weeks ahead.

I went to my monthly doctors appointment last Tuesday (I was 24 weeks). When she measured me, she said baby was measuring at 27 weeks. I have lost 16 pounds and am not gaining any back. She's sending me to have an ultrasound on Tuesday bc of the weight loss and baby measuring big. (Baby was measuring on track at my last appointment). I'm nervous and a little worried. I know it could have just been the way baby girl was laying, but my bump is way bigger than it was with my first, even with all the weight loss.