First Ultrasound and Scared

I had my first ultrasound Thursday at what I thought was 7 weeks exactly. Tech said I was measuring at 6 weeks 2 days.  Only saw a yolk Sac. The doctor confirmed that my uterus was indeed growing and everything looked normal. No bleeding or spotting. She said it may just be too early and to come back in two weeks. Obviously I'm freaking out a little seeing what everyone else has been able to see at this stage. Anyone else have something similar happen to them with a positive outcome?