When I was expecting my first DD I had a scan which he reckoned I was due 4th. I knew she was due 25th so the Dr said he would use both dates and talk about the date closer to when I was due.
She was born on the 25th and would have been in trouble had we waited.
Toward the end the Dr said the guy had my dating wrong.

If you know for certain when you fell pregnant speak to you Dr again and tell him your thoughts.

All the best in the the coming weeks awaiting your delivery