Baby is estimated 9lbs 3oz at 36 weeks 3 days. What can I expect him to be at birth?

I'm now 39 weeks and scheduled for a C section on Tuesday 6/21/16. A day after my due date. When I was 36w3d my Dr had be get an ultrasound to estimate how big the baby was because he's always measured large even when my Dr measured my belly with some tape. At the appointment, the technician said my son's legs were measuring 42w2d and his stomach was measuring 40w2d. His head was apparently so large the computer couldn't give a weight estimate because his head was measuring larger than a newborns. All tests have come out fine. I don't have GD. Dr thinks he's just a large baby. My Dr strongly recommended a C section and think he'll be well over 10lbs. My sister disagrees and says ultrasounds are wrong all the time. My husband and I curious to what other moms think. I was a premie while my husband was around 8lbs. Should we be expecting a 10 or 11 pounder?