Sunflowers can be hit or miss, particularly in this wetter than normal transition from summer to fall that we seem to have had. I wouldn't use any seeds that came in contact with mold. Try again next year and I'll bet you'll have more luck.

Next summer, you might want to let each plant only produce one or two big sunflowers by cutting away any other flowers while they are still small. That will put more of the energy into producing bigger heads. It will also give you all summer to ripen those two flowers. In the fall, when the flower petals have shrivelled and before our rains hit, cut off the flower, leaving enough stalk so that you can hang it in a sunny, dry, hot spot to cure. You should get the majority of the flower producing viable seed. (But watch out, for the birds will know when the seed is dry and start harvesting it themselves!)