Out of all my seedlings - and there are a lot of them, I have a couple things that have some green mossy type stuff on top of the soil. I scraped it off. I must have watered too heavily?

yep. that has happened to me

watering too heavily; not enough air circulation and a bit too little light.

scraping it off is fine - just keep an eye on it for re-growth.

A couple more with green stuff :p - the top is fairly dry - I don't water until it is dry down a little ways - I stick my finger in to see if it is moist or dry down below a ways. I have them under shop lights - just a few inches above the plants. Still - some are getting green stuff on the soil. Maybe move to a different type of container?

might need to. sounds like they might not be draining well enough.

the light might be too close