Yeah, those actually look much better than I expected.
Ok, hmm I agree with
@MonkeyPickAss I think you'd need to transplant to bigger pots - do this when the medium is dry. It'll be easier.
It could be your waiting too long between watering? Smaller containers would need watered more often. Essentially as the plants grow.
What's your temps while lights are on?
On a side note - solo cups are brilliant for seedlings, but technically after two weeks they're no longer seedlings.
Brilliant work, keep it up.