Baby growing

My ultrasound when I was 21 weeks said baby was 6 days ahead in growth went to see my obgyn other day and he said 6 days isn’t to much of a difference my due date is still the same Jan 23. He measured me by tape measure and says I’m measuring 30 which then I was 27 weeks 5 days he said when I see him next and I still am measuring big than we will do another ultrasound to see exactly the size of baby Incase of needing a c section or not. Has anyone have this happen before? My first child was almost 8 lb my second was 7 lbs