Did I murder my seeds?

Hey guys, long time lurker first time poster. I love the community, tons of help and always friendly. I tried growing for my first time this year but my germinated seeds didn't sprout or live for very long in a propagator I bought.

Im trying to figure out what I did wrong, I carefully transported the seeds and the soil I used was Daltons Seed Raising mix with nothing mixed in with it. I placed the germinated seeds into the soil about 5mm deep.
The propagator was left in the sun for a week without having the lid lifted off, could this have killed the seeds and 3 seeds that sprouted then died?

The seeds were from Attitude and I germinated them using the wet paper towel method - which worked perfectly. I waited until the tails were about an inch long before they were put into soil.

I was hoping someone can point me in the right direction and tell me how they couldve died. I have been guessing the soil was too rich but how can I tell? On the bag it says it has coco fibre and a wetting agent in it, im not sure if this could have anything to do with it.

Any help would be really appreciated, thanks guys

I used to start clones in a 5 gal. bucket outside in a bright but shaded area. I would put a shower cap over the bucket, & used root tone. Worked great in the warm months.