Boy or Girl

I had an ultrasound yesterday to see want I was having. I am set on that I am having a boy since I have two already and my husband has two has two from an other relationship. Today we open up the envelope with the boys and I’m not sure it’s a boy. I think know what pee pee looks like I had two boys already. Has anyone had this happen before and it turned out to be a girl? I’m ok with either I just want to make sure before I got out and buy stuff a boy.