Fungus on my potting soil! Need advice!

I have been putting 3-5" tomato seedlings started in Jiffy peat pellets into 3" peat pots. I have mixed up my own potting soil (peat moss, perlite, garden compost, Espoma Garden Manure, local sand and greensand). Now a few days later I am getting  some kind of wispy white fungus on the top of the soil - a lot of it. I scraped it off, but it it is coming back. I'm worried about damping off. I used bagged potting mix on some other seedlings and did not have this issue.

Any advice on potting soil? I could just use peat, sand and perlite, but there are little if any nutrients in it. I'm trying to stick to "organic" if I can (this is why I am not using the bagged mix, and also for cost reasons -- I have hundreds of seedlings). These will be going in the ground mid-May, and some will be traded at a plant swap.

Thanks!