3rd ultrasound but measuring 2 days behind?


I previously have lost two babies with a missed miscarriage. Both around 6-7 weeks. I'm now 8 weeks and 3 days and had my 3rd ultrasound with a fertility specialist not a sonographer. She measured the baby to be 8w1d when my first two scans matched perfectly should I be worried that this is the beginning of a missed miscarriage if it is going to stop growing? Or is it ok to suddenly measure a few days behind. Or maybe as she isn't professional with doing ultrasounds she may have measured Bub wrong?

Ahh I can't help my nerves!