Measuring late; worried about miscarriage.

I had an ultrasound on monday and my ob told me baby was measuring 6wks 3dys with a heartbeat of 127. My lmp was May 10th. I got a positive on June 15th(which would be a few days after ovulation if i was 6wks 3dys.) So that makes absolutely no sense to me and I'm worried about losing this baby. I'm considering messaging my doctor with my concerns but I'm worried that I'm just overreacting. 🤦🏻‍♀️ I have had 5 miscarriages before I had my first child.