I'm with Jodi... leave it as is.

I had the same thing happen at my 20 week scan by the way, bubs was measuring 21 weeks. Unlike you however I was counting days religiously and know pretty much exactly when I ovulated, so I know my dates are right. Looks like I'm just gonna have a big bubba. I was 9lbs when I was born, am now 175cm and 70kgs. DH was 7lbs when born, now 190cm or something (6'2") and 100kgs. Two large people = large baby I guess!

I'm not too concerned. My mum birthed me at 9lbs, breech (one of my hands/arms and my bum came out at the same time ), naturally.