I actually disagree with all this mystery sex stuff. When you've got a few growing i think with some instinct you can usually tell, my guesses were pretty much on the money. If you look at the stem the ones with more furry or white hairy stems usually end up ladies, and the less hairy ones have grown into males in my experience. Also if you rub the stem with your finger and smell each plant, the more THC bud smelling ones compared to that planty smell males have can give you an indication. But as i said, you might need to trust your instincts as well and getting to know your plants very well.
But if you've only got one plant it could be a bit trickier...