Could gender sonogram be wrong at 16 weeks?

So I went yesterday to an ultrasound tech, not at my doctors office but where I work and they measured me at 16 wks, 3 days. I was 15 wks, 4 days according to my md but the tech took awhile to get the gender and then typed "Think its a boy" Do you think they could be wrong?? I was really set on a girl!!!!!!!