I'm so sorry. There's not much more you can do. Put it under the heating pad, trying to get contact with the heating pad on its back. If you can drape the pad vertically at the rear, place the chick against the warm pad. Then let it get some rest.
It might surprise us all and recover its...
Take you little chick and gently massage it's throat and chest area in a downward motion. Then you need to try to get some water down it by wetting your finger and dribbling some alongside its beak.
Has the chick been eating and drinking at all?
It could be a "failure to thrive" victim.