Measuring 6+2, thought I was 7+4, no heartbeat

Hi mamas!

Went for first ultrasound. They did both transvaginal and belly. Measuring 6+2, thought I was 7+4, no heartbeat. Any success stories out there of a successful pregnancy after no HB at first scan and measuring behind?!

Can I also get some help on understanding how my dates could be off. LMP was 11/20, thought I ovulated around 14 days later, and positive pregnancy test two days before missed period. I did have two chemical miscarriages right before this pregnancy. So my hormones/cycle could for sure be wonky.

Thanks in advance. Need some reassurance :)