I was very similar to you, i started to measure quite a bit more each week, and at one point i was 8 weeks ahead! I had an ultrasound so they could see if i had excessive fluid and was diagnosed with polyhydraminos and they estimated that my baby was a fair bit bigger than average as well. I stressed out waiting for my ultrasound and waiting to find out why i was so far ahead, and did some googling which was less than helpful...

In the end, everything was fine, i just ended up ginormous When my waters broke there didn't seem to be all that much more there, but the baby was huge!

Good luck while you wait for the ultrasound!