Is my sonogram confusing?

i am confused by all the mention of gestational ages and additions of 2 weeks - my periods were like clockwork, and i only had 2 days before ovulation and 3 days after. my sonogram dated as 8 weeks 4 days, and couniting back that actually does land on what would be my ovulation day - so i'm asking, as is said, does the sonogram take in consideration the extra 2 weeks, because that seems to be most impossible. thank you