6 weeks to 7 weeks ultrasounds possibly miscarriage

So we got pregnant off of fertility treatments. So we get early ultrasounds. I was measuring 6 weeks 2 days a week ago. Only had both sacs. Went back yesterday at 7 weeks 2 days and there’s a baby but she said based on my measurements it’s not where it should be and no heart beat. They took blood to check my hcg levels but she’s thinking a possible miscarriage but my body hasn’t registered it. I’ve never had a miscarriage and I’m holding on to whatever little hope that I have that maybe my fetal age is a little behind. We finally got our happy ending after dealing with 4 yrs of infertility to be taken from us so soon.