My tummy is measuring about 4/5 weeks ahead also because of fluid and bubs position. I honestly wouldnt worry yourself with the weight estimate as it is just that, an estimate. My DS2 was born 9lb6oz at 38+6 but his birth was great! No dramas at all. Im not overly tall or overly small but my hips are quite narrow compared to the rest of me but all was fine. Im sure bubs is just perfect :)