When can you truly tell gender/ has anyone ever been told wrong at first?

 I was told girl at 12 weeks (doctor said he was 80% sure) then went in today at 14 weeks and was told boy (doctor is 99% sure) . I was devestated and started bawling mid ultrasound..everyone in my family has boys I was praying for a little girl and I swore since I found out I was pregnant it was a girl. I don't think the baby was in a good position to see either compared to last time. I know I have to accept it's probably a boy but I have also heard of a lot of other women getting false results this early on and not finding out until later by German doctors. I was just curious if anyone else had something similar happen to them. Please don't get me wrong i am super excited my baby is healthy and I know I will love him or her either way I just wondered.