Due date got moved back, anyone else?

Anne C • 29 | Nurse | Mom of 1 💘| Due in Aug w/ #2 | two angel babies
So I went for my first ultrasound on Friday and thought I was 7w5d and I went to my doctor today for the results and was told my due date got moved back from October 9th to 21st! Did this happen to anyone else? We only BD on the 18th and according to that due date we conceived on the 29th...seems wrong to me. Has anyone had this happen and then at 12 weeks get changed again? 
This also means I got a positive test and a clear blue reading of 2-3 weeks at 2 weeks 3 days?