Baby measuring big?

Anyone else measuring ahead of schedule? Had an ultrasound 3 days ago, I was 15+3 that day, but baby was measuring a full week ahead at 16+4? It was during an ER visit so it was not my OB and he didn't seem to care that it was a week ahead at all, when I asked about that he said "Yeah it happens." And that was it. I've been waiting for a call from my OB office reviewing the ultrasound and ER visit but have been very stressed about baby's size in the meantime. Everything else appeared normal and he's a healthy baby otherwise.