A couple of possible issues jump out at me. Not necessarily in order - "really thin and die within a couple of days" might be from (1) insufficient light (1-1/5" above max.), (2) not under the lights quickly enough (start them under the lights), (3) too much heat from either heat pad so too hot soil or high air temps can both cause this (I'm assuming they are off the heat as soon as they break the soil surface), (4) over-crowding the plants as in starting multiples in the same small container and then not transplanting them quickly enough to separate containers, and of course (5) over-watering which kills more seedlings than all other causes combined as roots rot and damp-off fungus develops.

Then there is "the dirt seemed dense and the water kinda laid on time for a bit". Most seed starting mixes are primarily peat based and the so-called "organic" ones especially so. It must be well wetted (soaked and then wrung out) to begin with as peat will repel water if dry. Personally I don't care for the "organic" mixes for 2 reasons: (1) they aren't any more "organic" than any of the others but just cost more and mis-lead users, and (2) they aren't sterile so contain many more potential contaminants and bacteria that can cause problems.

I'd suggest turning down the heat on the heating pad and remove from it ASAP, cooling down the room, uncover ASAP as sprout or better yet don't use a cover, get your lights closer, wet the mix better to begin with and then cut back on water and try bottom watering instead, and use a different mix.

Just some things to consider.

Dave

Hi Dave! Thanks for replying!

I grow in separate containers, usually the little black plastic ones cut into sections of 4 with 1-2 seeds in each. Then I keep those in a big plastic tray and that's what sits on the heating pad. Then as soon as I see them break dirt I move them under the light (off the pad)

Everything is in my basement store room, so it's a pretty cool room to begin with.

I've seen people say use a fan for better air circulation, so I might try that.

Way to late for any vegetables now, but I'm going to retry with some herbs. I'll take all your suggestions into account. Thanks for your help!

Then it sounds as if you are on the right track and it would seem the mix may be the issue. Then again basements often tend to be havens for molds and such so you might want to check out that possibility. A fan is a definite plus.

Dave