Girls, please tell me how you feel about ultrasound when they say the…

Girls, please tell me how you feel about ultrasound when they say the baby's sex? Have you ever had an ultrasound mistake? At 19 weeks, my second screening showed a boy, I think they could have made a mistake or should I wait until 32 weeks? I was told girl at 38 weeks with my first child, but he was actually a boy ?