confusing gender ultrasound

Hey everyone so I had an ultrasound today I am 16 weeks and had an ultraasound through a private place at first they were like it's s boy then the baby moved and she said oh wait no that's the cord and then the baby open up legs wide and she said oh nope it's a girl but then printed pictures out and was like wait I'm not sure so I have another one on Thursday so I just felt sad lol but they showed me the pic and said that they most likely think it's girl because what they thought was boy is too big to be a boy part so hopefully Thursday I know I had a question can skull theory be used on 16 weeks?