Baby measuring 11 days behind

Regina
I just had my first ultrasound at 7weeks5days and the baby is only measuring at 6weeks1day. We heard a strong heartbeat and the doctor didn't seem that concerned, I'm going back in two weeks for another dating ultrasound.
I only had two periods before conceiving due to nursing, and they were about 31 day cycles. The doctor thinks that my cycle was long. 
Has anyone had such a large gap? I'm worried about this meaning that I'm headed to MC
 With my first she measured about 4 days behind at the beginning, then caught up, and then was about 2 weeks behind the last month at the end. I was induced because of suspected IUGR, and baby ended up weighing a very normal 6lbs 11oz and the measurements were off by almost a pound. 
Any positive stories?