Missed miscarriage questions

Mimi • Baby boy born in April 2020 👶🏼 loss in 2021 👼🏼 rainbow baby coming in 2022 🌈

I was told a couple days ago that I’m experiencing a missed miscarriage. The baby measured only 7.5 weeks when we thought we were 9w+2d, and they couldn’t detect a heartbeat by transvaginal ultrasound.

I had my HCg tested the same day and it came back at about 20,000 (which would be normal for a 7.5 week pregnancy). Is there a chance that my dates are just off? Wouldn’t my HCg be a lot lower if the baby stopped growing 2 weeks ago? I’m scheduled for another blood test today, so we’ll find out on Monday if my levels are dropping, staying the same or rising.

Just curious what other people’s experience has been with this?