Hello everyone! Girls, please tell me — is the pregnancy term in weeks…

Hello everyone! Girls, please tell me — is the pregnancy term in weeks calculated from the first ultrasound or from the last screening ultrasound? I don't remember the date of my last period. Today I was at the gynecologist; she calculated 35 weeks 5 days by the first ultrasound and 37 weeks 2 days by the last ultrasound. It's making my head spin — what's correct, if you know please tell me. Also you need to take covid 19 tests and without them they won't admit you to the maternity hospital.