hmm you might have gone wrong with the good organic soil with such small seedlings. Maybe not it depends on strain. Did you mix perlite in with it.

for my seedlings i use a mix of 50% perlite and some peatmoss and sand

as for light. The best way to figure it out is to find the lumens per sq foot

your plants will die with less than 2000lumens/sq foot. 5000 is ok
and 7000 is optimum. the watts arn't as important as the lumens. So find the area and find the lumens. But you will need more light once they get bigger. Right now they are fine.

Also watch the heat. Heat stress can look ilke nute burn. so keep your heat below 85 F