Dates not making sense to me

Hi everyone

Hoping for advice. Went in for ultrasound thinking I was 8 weeks. I am measuring 6 weeks 6 days. Heartbeat 145. So the tech said everything is great and not to worry about measuring behind.

But I went back through the app and I got a positive test on April 12. That’s almost 4 weeks ago. Would it have been possible to get a positive test if I was only 3 weeks at that point? Plus my periods aren’t that irregular so I’m surprised I would have ovulated so late. Lastly I’m not sure my BD days would line up!

I see the doctor Friday so I’ll make sure she’s not concerned but I’m curious if this has happened to anyone else or if anyone has any thoughts.