i wouldnt worry - my ob last time and my ob this time said anything plus or minus 2 weeks at this point is not a problem at all.. and that scans etc are inaccurate
i know it is hard not to overanalyse and think about it all but dont worry at this point.
enjoy having another look at your gorgeous bub!!

ps have heard so many stories of ppl being told will have a 10 pounderonly to push out a little 7 pounder and vice versa