two different due dates??? which one do I go by

Irma
I was given TWO different due dates. According to my Dr. my due date is  04/03/16 but according to the ultrasound tech that did my 4d ultrasound based on the babys weight and size my due date is 03/20/16 I am currently 32weeks & 3 days according to the dr., but I am 34weeks & 3 days according to the Ultra sound tech. Which date is my due date? Please help me out ladies I'm a ftm