At 8 week scan baby measured at 6 weeks?!?! Any experienced this?

MsSingle

I had a scan at 8 weeks and baby is measuring at 6 weeks. There was a heart beat and everything looked great.... for 6 weeks.

Midwife said it was just that my dates were off. I explained that this is a donor baby so it's not as if I was having regular sex and just "caught on" a few weeks later. I know exactly when insemination happened (20th June) and if the scan is correct for dates then fertilisation would have happened on the same date I got a BFP. That's just not possible.

Just wondering if anyone has had any experience of this. Did baby catch up? Did it end in a loss?

I've had 2 miscarriages before so I'm expecting a loss tbh.

Photo is what I was given from the scan, I didnt ask for it and tbh I cant really make anything out but I'm grateful that they gave it to me.