Baby's Gender

Alize
Okay so I'm 13 Weeks & 3 Days as of today (7/12/15). my doctor told me to come in July 20th to find out what I'm having . And Me & My boyfriend wanted to know how accurate would it be? Is it too early to find out? Can they be wrong? Or since I'm 3 months would it be accurate? We just really wanna know & be 100% sure