You will need to check where the leaves meet the stem for calyxes. If you see a little tear drop shaped thing with 2 white hairs coming out, it's a female!
If you see a rounder ball shape with no hairs, it's a boy. If you think it's a boy because you see a ball, wait a few days because the hairs may pop out to know for sure. Male parts grow in clusters too, dead giveaway if you have "a bunch of grapes" think going on.