Alright, I don't know vivosun lights but if I put my, viparspectra xs1500pro(150w) at 12" with 75% i would burn my seedlings for sure!
12" is good a good height but I would back up to 50%, but you will see soon if your plants will do good, don't stress em this early. If they can take it, let them thrive, if not back off.
200w for the whole grow in a 3x3 could be enough. I'm using a 480w in my 3x3 but also grew some average buds with the 150w in there. Do y use any ppfd meters or the photone App? Ppfd range for seedling is around 100-300 in the early stages.
Cheers, keep us updated