Finding out gender soon, worried about dissapointment

I really dont want to be dissapointed, but I feel like i wont be able to help it. I already have a girl and I want a boy so so bad. I know in the end ill be happy regardless, but i cant help but get upset thinking that I wont get a son, especially since my SO only wants 2 kids. I saw a glimpse of a scan i had at 16 weeks and swore i saw 3 lines but the ultrasound tech said the legs were crossed.. ive been feeling down ever since cause i swear i saw it. Just needed to vent, but Any advice? :(