Over watered or poor temperature? Can it be rescued?

if it didn't dry out, it should recover, but if it did it likely died. first, you need some sort of amendment to help with drainage and aeration -- perilte, vermiculite, something. mix at 1:1 with soil and sphagnum peat moss or 2:1 with coco (need less with coco). This will help with seedlings too.. virtually impossible to overwater at these ratios. second, change your perception of watering. You water the entire pot. A little runoff in soil is fine to ensure the entire thing got wet. In soilless you get 10% runoff every time and fertilize everytime. First irrigation for each can be water-only. Now, 3-inch ? pots you have should remain moist enough for 4-5 days minimum. With seedlings, i'd water at first sign of superficial dryness, but again.. always water entirety. you don't want a nascent root drying out.. if you see roots at the bottom, this is no longer much of a concern. Later on you want to let it dryback more as this reduces pathegen and pest risks as well as promoting deeper roots. If you water superficially and incompletely, you promote superficial roots as well as other elevated risks. Can use loss of weight to dial in how much water you need each time if you have to pre-mix nutes etc. You'll learn that as you go.. will be consistent as long as you stick to these habits. You don't pick the volume of water, what constitutes your substrate and how dry it is determines the volume needed... and at least 10% more for soilless context. you'll find out soon enough if they are alive... stick to the above and you won't be the cause of a seedling dying. Some things are out of our control. If in a cold climate, like me, a heat mat is useful.

Looks like your medium was kept too wet for the poor little seedling. At that stage they do not require much watering at all, just enough to get the soil most. They have no root structure to absorb much water out of the soil so the soil will stay wet way longer then you would think. I would let your soil dry out a little. Moving to better light and stable temps is always better for seedlings. If this is any older then 2 days from sprout then your seedling is very stunted. I hope this helps.

Looks like it has dampened off. Was kept too wet.