Early gender.!

Hi. I'm just currently turned 14wks on yesterday and I went to an ultrasound facility to find out the sex of my baby early. I was told the baby is a boy but I had som many signs for it being a girl and I really thought it was a girl. Has anyone or know of anyone who experience finding out the gender early and after their 20wks the gender was different. I have already have two boys and my pregnancy is sooo different from when pregnant with them I just knew this baby was an girl.!