the heating pad mite be making ur grow room too humid,make sure u got frsh air circulating so the water evaperating isnt lingering in the room.wait till u got a couple "true"(spiked) leaves than transplant,and also lights need to b a lil further for seedlings.
u should also mix ur own soil and keep the nutes down till u have a more developed plant then give it more-HOPE THIS HELPS,GOOD LUCK