First dr appt. 6 weeks 2 days.

I went for my first visit and they were not able to see the baby yet. They think I'm 5 weeks instead of 6. But everything looks good. I have a heart shaped uterus, and had a miscarriage 2 months ago. But I do have a 18 months old!! Has anyone else been through this? I go back in 2 weeks for another ultrasound. The dr said not to worry!!