Sorry about your bad luck with the seeds. Maybe they were just a bad batch, I don't know. Don't give up on those others, though, till you're sure they are dead.

Get rid of that heat mat with the seedlings. Keep them at or just below room temperature. I have had good success getting females by keeping them on the cool side (65-68) for the first three weeks of their life.

If you do end up with a male and female consider making a batch of seeds for yourself just in case of emergency and as a way to store genetics. When you get to that point I will be happy to help you.