Hmm you kinda saved me I think. Starting my seeds shortly and have a heat mat. I have touched it a couple times and thought it was kinda hot and never put 2 and 2 together. I've been having poor results my past 2 grows using this heat mat.... lol -.-
It's not the mat but the misuse. The mats help prevent damping off, speed up germination and give a healthy start BUT it is not a plug-and-play gig. The dome has to monitored and removed, replaced, vents opened/closed. Misting regularly is a must if humidity is low.
On the other hand I clone by cutting, putting the stems in plain water and waiting for root development. Once roots are out into a root shooter (these days) and at the edge of my veg lights, then moved in closer daily. By the time they are 3 weeks they are out from under a cap under a 1000 HPS, 4 fluoros and 2 side CFLs.
Use a gallon jug with the bottom cut out like a baby greenhouse. Use the cap to control heat & humidity and here's the lesson - the same thing happens under those domes that happens to unmonitored seedling domes with heat mats. Leave the cap on when plant is small and you're not watching and it keels over and dies like a dog left in a locked car with the windows up. Tune into your plants.