confused ?? any insight on this

so i got a dating scan December 1st and was told i’m 8 weeks 2 days.. could not go off of LMP because that was September 10 and i would’ve been like 12 at the time(irregular periods) so assuming the dating scan is accurate, i’m due july 11. everyone that is also due july 11 conceived between the 17-23 or so… but when i count on the calendar those dates from when i could have conceived (which i have no clue)until december 1 it counts about 6 weeks. so how would i be two months already from mid october to december 1 ? do you think i could’ve conceived the first week of october because then that would actually be 8 weeks. but my dates don’t match with anyone else due july 11 so it’s just throwing me off 😩😩 thank you guys in advance.