Where are all the other fish you had?
When you treat ich, unless this fish has never been in your main tank, you must treat the entire tank, even if you only see ich on one fish.
Still, you have overdosed. Please do a 50% water change right away.
When you do use salt, you must dissolve the salt in warm tank water in a cup. Then, you add the salt to the tank over a period of a few days to let the fish acclimate to it. Did you dump it all in that tank?