If my ultrasound said i was 9 weeks 3 days pregnant on april 15, 2021 what would be my conception date ?

Conception is calculated 14 days after the first day of your last normal menstrual period , if the sonogram said 9weeks and 3 days on 04/15/21 you most likely conceived about 7 weeks and 3days prior to that date ,keeping in mind that the sonogram can be a few days off. The whole pregnancy is 40 weeks starting from the first day of you LMP ,so is better to correlate both dates and size.