Question regarding us dating-my last period was november 30th, 2020-putting my due date at september 6th, 2021.after dating scan the edd was sept 9th (ovulation dec 17th), how is it possible if my so&i only had sex on the 18th. is it normal to be off?

Yes it is normal, your due date is estimated meaning you can have the baby any time 2 weeks prior as well as 2 weeks after that, so your sonogram confirms your due date.

Ultrasound dating is always with a certain margin of error it’s a bit less of inaccuracy the earlier you are but there’s still only a range regarding dating a pregnancy so it’s not uncommon for there to be discrepancies. What you described as well within the margin of error of the machine