nice so the curling was starting because humidity was too low? seedlings want 60+ right?
Temps on that side are usually 82-89 with humidity 40-50. Temps on the lighter shades of green side are usually 84-92 with humidity 40-50, but that small increase in temps demand more humidity.
So humidity or temp is out of spec, whichever is easier to control. For me, it is what it is right now.
Between 60-80 for seedlings as long as temps are between 70-85. Lower humidity or higher temps and it's just a VPD thing. Higher humidity or lower temps and it can damp off.