just make sure after germination that there's plenty of soil depth beneath for the tap root to penetrate 4-6 inches. this may be one of the bigger factors. I've had 8 straight females focusing on this rather than 5 straight males I had before. And definitely make sure you're actually seeing males; the plant should be 8-12 inches tall or have 5 or so nodes going up before you want to know the sex. If it is actually a 'seedling' like you say you might be mistaken when you say it has male balls already