If it is splitting down the middle and has a hair (pistil) sticking out, its a girl.
Male flowers usually grow on a stem, although the stem can be hard to see at first.
Week 7 in my diary "cannabis conundrums" has pictures of male and female primordia (pre-flowers) if you are keen for any other references that may help you identify what is going on with your plant.
Also has many other pictures of interesting things associated with cannabis, from the weird to the wonderful!
Disclaimer.........
(For educational purposes naturally, I would not want anybody, including myself, to be doing anything prohibited!)
Hope this helps, Organoman.