Could well be a male flower, if it is a seed, it should be easy to peel open the calyx and find a whitish/greenish/light brown seed inside.
Have a look at my diary "cannabis conundrums" and in week 7 you will find pictures of male flowers and this may help you to identify this particular growth more positively.
If the plant was grown from "bag seed", this shows the risk of growing "bag seed", as generally they come from hermaphrodite female plants, which then pass on this genetic trait, to become hermaphrodites, to any seeds produced this way.
Hope this helps,..........
Organoman.