Imo, you overwatered. Once you have seeds that have cracked and planted 1/4" deep in soil, they should NOT be watered/sprayed at all for at least two days, depending on your temps at soil level. Hot temps will dry the soil quickly on top, but not much down an inch or two into the soil. Stick your finger down into the soil about an inch. If any moisture is felt, its too soon to water.

Another means of telling when its time to water is to physically lift each pot/cup right after a full watering, then, in a couple/few days when they get really lightweight from lack of water, its time to rewater. peace and good growing