Wow a gender scan at 12 weeks, that's very early. I don't think I would trust it if I heard girl because the boy parts might just not be visible and could pop up on the next scan, lol. I know someone who found out she was having a boy at 14 wks so I suppose it is possible to tell that early.
I know I have to find out the gender before the baby is born so I can deal with any gender disappointment.