Measuring 3 weeks ahead

Kasey
I had an ultrasound today that estimated weight at 7lbs with a due date of 7-3. My actual due date that was given to me at the beginning of pregnancy is 7/25. 
My doctor doesn't seem concerned at all and said it's just an estimate (but the whole reason I had the ultrasound was to check size because my first child was big and my stomach is huge). However, he is making me redo my glucose test next week. I passed it when I was 27 weeks. 
Anyone else experiencing or have experienced this? I really would like a vaginal delivery and not have a 10 lb baby!