No Heartbeat at 6 Weeks—Please Help

I went to my doctor yesterday at (which I thought) 6 weeks + 1 day. When she did my ultrasound she said I was measuring more at 5 weeks and a few days and that we weren’t able to hear the heartbeat yet. She said everything else looked like a healthy pregnancy, but I am to come back in 2 weeks to make sure we hear a heartbeat.

Has this happened to any of you ladies before? I don’t know how I could be off by a few days as I knew exactly what day my last period started.

I’ve had a miscarriage before so I’m scared to death something is wrong.

Anything you ladies could tell me would really help!

Thanks!