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When I start seeds and/or cuttings, and see a green moss substance on top, I know I am overwatering. Additionally, overwatering can lead to "damping off" which is a fungus, which usually results in the seedlings turning dark and wilting at soil level. I don't know where you are, but if you have the time (planting out wise), I would restart some more seeds, and this time, go easy on the watering and find a spray containing sulphur, (a million offerings out there, and I dampen the soil on seedlings when first starting, with such a spray! Remember also, you are dealing with a "cool weather" plant. Cheers!