Any mommas had this happen?

So I went in for a 34 week routine check up. Every check up they measure my belly. I always feel that everyone tells me I look big, and that my baby is going to be HUGE for how far along I am. Well this time they measured me at 39 weeks?? They sent me down for a fluid check and a growth scan and confirmed fluid was perfect and baby is measuring at exactly 34 weeks and 5 days and weighs 5 lbs 4 oz. --Also everything is formed correctly and no health issues with baby... SO CONFUSED??? Does this mean my baby is possibly further along than we think? Could be born earlier? Not enough torso room? Or just a big baby and the sono is off? FTM here, help me out ladies :(