HELP!! Scan and dates dont match!!

My last period began on the 12 September, meaning I should be 8 weeks 1 day pregnant today.

I’ve been for an early scan last night which says I was measuring at 6 weeks 1 day, baby was in the right place and had a

heartbeat.

I got 3 positive pregnancy tests on 9th October including a digital, which said I ovulated 1-2 weeks ago.

But if my scan dates are correct I would have ovulated around 10 October, 1 day after I got a positive pregnancy test....

Can anyone explain??