Confused on how many weeks I am

Charlotte

I posted yesterday in regards to having a scan done and they measured me at 8 weeks. From all the dates and what my midwife said I am 7 weeks. They found no heartbeat and due to them measuring baby at 8 weeks they said this is a missed miscarriage. However the gestational age on the scan says 6w5d. I’m confused? I didn’t think I’d be able to be 8 weeks as my last period was 7 weeks ago or less so 6weeks 5 days makes more sense to me.