I fermented apple juice to make cider, but the apple juice might have had mold growing in it...?

Actually, mold is not that great a problem. Just skim it off. Next time, use potassium or sodium metabisulfite (Campden tablets) to kill off any microorganisms in the juice, a day before you inoculate with your cider yeast. And be very careful about sanitation. You can re-contaminate the juice very easily. BTW, I hope you didn't try to use bakers' yeast.