Boy or girl ?

So it's been confirmed by ultrasound that I'm having a baby boy. She had at first said it was going to be a girl then when baby finally opened its legs she realized it's a boy. I'm just concerned because everyone... I mean everyone except my mother in law still says they think it's going to be a girl. They say it's because of my belly size or things like that. It might be a Mexican culture thing to believe that.