Ultrasound

I had an ultrasound a few weeks ago and they measured me at 6w3d.  That was 5 days behind what I thought I was. I have another ultrasound on Wednesday.  I am wondering how many of you actually turned out to be farther along then they thought you were originally in a later ultrasound?? 
I'm normally pretty thin and the way my belly is growing at just (almost) 9 weeks makes me wonder if I am a bit farther along then they thought.