I’d say more holes and less water. Plus better air circulation. Some of the veterans will chime in. Good luck. Never personally had that issue. Happy grows.
Burnz

Could be mycelium, is that soil and can you take a picture in a different light

I wouldn't get too stressed. Probably just fungas from the soil being too moist. Looks like Dog Vomit Fungi (which isn't harmful to your plants). If you have good root structures just pop the plant out of the cup. If you don't have many roots (you should at 3 weeks) cut away half the cup and bottom, using the remaining cup as a "trowel" holder and pick out the mold. Then use H2O2 to spray down the effective area and transplant into a pot, sliding the rest of the cup out. This will hold together your roots without all the dirt falling away and the cup will just slide out of the new pot.