I have always measured big for dates. It freaked me out in my first pregnancy I went for my 30 week check up and I measured 36 weeks (before that I'd been about 2-3 weeks ahead). The Dr was worried so we went for a scan but she was just a big bubba. She weighed 8 pounds when she was born at 37 weeks.
This time I went for an appointment at 19 weeks and measured 22 weeks but the scan I had a couple of days before said he was right on for dates.
Your baby may just be a good size. What weight were you when you were born that is often indicative of what your baby will weigh. I was 9 pound at 38 weeks.
HTH
Tracy