doctor being difficult help please?!?!

Measuring 3weeks early yet. Which would put me at 37 weeks & 4says today. If they changed due date. Doctor's office is refusing to change my due date. 😣 Which means I'm still not die till 12/23/16 even after us already having an ultrasound done. To see how big our girl is. I'm terrified of a c-section. She wants us to do another. Ultrasound if she's big at next visit next week. Is this normal or should they change my due date? I mean I'm weighing in at 175.4 pounds as of today. Our 1st child was a big baby. He was 9pounds but had him in FL. Carries him to 41weeks. Having her in PA. I'm starting to get worried & anxious at the same time. Any advice would help?!?!