Accuracy at 11wks. pregnant, going by the actual age of pregnancy can it be possible for the ulstrasound to date me 10 days before i even had sex with second partner and 1 day after my first partner?

Evidence suggests that ultrasounds more accurately predict your due date than using your last menstrual period—but only in the first trimester and early second trimester (until roughly 20 weeks). Early ultrasound due dates have a margin of error of roughly 1.2 weeks. After 20 weeks, your Dr will measure your fundal height to see if the baby's growth is keeping on track with the EDD.