Super confused, can someone please tell me when I most likely conceived??

Im so confused. I found out Feb 12th I was pregnant, I got a faint line then BFP the next day. Going off my last period which was Jan. 18th-21st I was estimating 7 weeks 5 days today (March 13th) I had an ultrasound today and they said the baby was measuring 6 weeks 5 days so a whole week earlier than I thought. My app says I ovulated on the 8th which I did not confirm but going back from 6 weeks 5 days would make sense and mean that I conceived on the 8th right?? Here’s where I’m confused, if I ovulated and or conceived on the 8th how in the world would I get a positive 4 days later?? Impossible and doesn’t make any sense. I had to have conceived some time before the 8th but if I did wouldn’t I be just a little further along than 6 weeks 5 days? Does that mean the baby is measuring small or? Maybe I’m missing something I’m not very good at calculating stuff like this when it comes to my cycles but here is a screenshot of the month I conceived and all the dates I had sex in the beginning of Feb. I didn’t have sex at all in Jan. When do you think I conceived? 🤔🤔🤔