Larger gestational sack?

So I have PCOS and I got a negative pregnancy test on February 13 but a positive on 14 February. I’m supposed to be six weeks now but I do have high HCG levels early on. With my other three children I had a positive pregnancy test like seven days after intercourse. I got bloodwork on 15 February and my hCG was 41 & on 19 February it was 390. I don’t know exactly when I got pregnant because I haven’t had a period in 7 months due to the PCOS. I got an ultrasound and around this time with my other three children I seen a fetal pole and heartbeat. Has anybody had a gestational sac that was a week ahead of the baby? I thought I conceived on the 2nd but now I’m thinking it was the 6th or 7th maybe but the sac is measuring 5 weeks 5 days. Any opinions?