Accuracy of Gestational Age

Hi Mummies. Just wondering if you ever had doubts on the dates of ur pregnancy? I’m in a LDR, so the window period for pregnancy is significantly narrowed down to a specific date when I have intercourse with my hubby. Initially, dr said i’m 10wks. But seems like the pregnancy term moved agn? Its now 11wks? I understand dates are calculated based on size of fetus, etc. But is there a possibility for the baby to grow faster than its supposed to during first trimester? Or should i challenge my dr in terms of pregnancy duedate? The thing is, i haven’t had much of appetite until much recently, but my overall weight seems to have come down by 1kg+. So we are really confused as to whether the pregnancy dates are correct. Should i be concern? Coz my dr told me i can start taking multivitamins, etc and stop folic acid by wk12. If the dates not accurate, will this have an impact to the baby?