Has sonographer been wrong?

So my last US I was 16 weeks and the sonographer couldn’t see if boy/girl so she made me go walk around and come back and when she did it again, she was almost positive it was a girl but it was very quick. Mind you, as she was scanning the first time she went over a few times to try to see if it was a boy and I saw something but it could have been the cord. She gave us a scratch off when we left because we didn’t want her to tell us there so when we got home we scratched it and it said girl, my fiancé thinks she gave us the wrong card 🤣 because it was dark in the room but is there a chance she could have been wrong? I go next Saturday for my 20 week scan.