Ultrasound date confusion, help!

Lachelle • Fri, Jul 13

If I am supposed to be 6 weeks 3 days from my lmp so why am I measuring 5 weeks 1 day and only 4.4mm on another scan. I ovulated on the 17th on June so that would be 3 weeks 4 days today so does this mean the ultrasound is measuring from conception, I am going to have a miscarriage, or whaaaat I’m losing my mind. Please explain.