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 ?