Measuring behind?

I had my first appointment today. Based on LMP, I should have been 7 weeks 2 days. I thought I was 7 weeks 4 days because I had ovulation signs a few days early. My midwife wanted to do a belly ultrasound just for fun, and she said from her experience looking at the size, I'm measuring a week of two behind and it was so small we couldn't tell if there was a heart beat. I'm so scared. She seemed hopeful and I'm scheduled for more blood work and possibly ultrasound in the next few days/week. Has anybody experienced anything like this and had a positive outcome? Please no miscarriage stories. My heart can't take it.