Measuring 8 weeks and 4 days

I went to the doctor last week and my doctor told me it wasn’t good news because I was supposed to be 9 weeks and 4 days based off of my last period and I went and got another ultrasound today and measured 8 weeks 4 days but she didn’t see a heart beat. She said it could be because of the angle but to prepare for a miscarriage. I’ve read several stories where this happened and a heart beat was found a couple weeks later. Has anyone else experienced this?