Curling leaves dark green

if you have been feeding from start, stop... only give water for a while. Those symtoms don't look like it's kinetic in nature, lol. i.e. because it fell. definitely the hot soil you mention. stop adding stuff.. it dosn't need cal-mag at this age. a seedling doesn't need anything but moist substrate for 2 weeks or so. you first reaction should always be to do less.... never add anything unless oyu are 100% certain, or youjust create a new problem or throw kerosene onto a dumpster fire.