8 weeks but scan only 6 weeks :(

Based on the first day of my last period, I should be 8 weeks. But when I go for my first gynae appt at “8 weeks”, the ultrasound measured only 6 weeks. During my 2nd appt, supposedly 8 weeks based on first ultrasound, it then measured 9 weeks during the 2nd ultrasound. I asked my gynae and she explained that sometimes the ultrasound can’t measure accurate size while it’s still small, so usually need a few appts before can really tell the exact week you’re in.