FWIW, DD was a surprise, and two different techs and the midwife used "he" a few times as well as "it," and we were sure it was a slip, but the one tech said she just didn't like "it" too much. I was *SURE* dd was a boy and I analyzed our 34 ish week ultrasound with a fine tooth comb and both DH and I really thought we saw boy parts, but we also kept the "it is a surprise mantra" and had that attitude.
I wouldn't be so quick to assume . . . if you want to surprised, you still can. At any future ultrasounds remind them that you want to be surprised, and maybe you will be.