Measuring behind on Ultrasound

Ca

My last period was 9/6.. So, I should be 6wks4days. I had an appt with my OB last week and she said bc my cycles have been 32/33days that I could measuring earlier. With my daughter I also measured two weeks "behind" so I'm not worried about that aspect.

I had an ultrasound today, and she said everything was healthy, normal, there's a sac & yolk, and no threat to the pregnancy. But she said I am 4wks6days. The only reason I'm concerned is bc I had a positive pregnancy test on 10/4. That would have made me 2wks2days pregnant??? I didn't think that was even possible... Any thoughts? I have another ultrasound two weeks from today. The tech was very confident that a fetal pole was just on the brink of forming and felt very positive about the pregnancy.