Why did my 9 week scan change my lmp date? did i ovulate late. is that what happend? is dating scan at 9 weeks accurate to find ovulation?

Scan likely accurate: A 9 week scan should be accurate at getting our best idea of a due date, although it is within normal range to deliver anytime between 37 and 41 weeks....so even our best guess isn't that "accurate". And yes, if the scan made your due date later, then you likely ovulated later. Ovulation time can vary even with fairly regular periods.