Seedlings really don't need anything to eat,, they bring their own food in them feeder leaf... Well called cotyledons. Is always best to never feed anything to a seed.. And most dirt has a 'Starter' charge of fert's. I'd try flushing it next watering if you want to try to save it.. I don't ever have to fertilize a plant in veg stage. The biggest mistake people make with weed is over fertilization. People tend to forget fertilizer companies are out to sell product. But I don't feed unless they look hungry in veg. Now flower, they need alittle food. Thats just me... I've burnt seedlings even with all oganic ferts. The are delicate.. At that stage all they have is a tap root with very little rootage... Easy to burn them root tips. GL and Keepem Green