I recently had a baby. my due date was 11/13/2020. i didn't have a period in february. my ultrasound scan on 03/23/2020 shows that i was 6 weeks 3 days on that day. my ultrasound tech told me i got pregnant on february 14th 2020. when did i conceive?

Date are estimates: Dates are just estimates, and a few days does not make any difference in almost all cases. One can just get a calendar and count backwards 38 weeks from the estimated due date (38 weeks from 11/13/20) to see the estimated conception date, plus or minus 1 week. The exact conception date of a natural pregnancy is never known because nobody can tell when the sperm entered the egg.