basiacally instead of the little cone that the pistils come out of there will be a small grouping of little balls at the joints of the stems and if you have that then it will definitly be male, but i couldnt help but notice the tips of your leaves are browning and curling, that could be heat stress or nutrient burn. If your lights are closer then 2-4 inches you might wanna back em off a little bit or go a little easier on the nutrients and see if that doesnt clear it up, the stress could cause your female to switch to hermie