I just registered for prenatal care last Monday. I didn't register on …

I just registered for prenatal care last Monday. I didn't register on time because I travelled for my father's funeral, but when I registered, the doctor examined me and told me I registered late, which is bad. He said I was 25 weeks and 3 days pregnant, but the scan told me I was 21 weeks and 5 days pregnant. I showed the doctor the scan results, and he examined me again. It showed 25 weeks and 3 days now. I don't know who to believe anymore because the scan predicted the delivery date to be May 29th, while the hospital says April 30th.