Sounds like you are doing the best you can. No one can ask more from you.

I once read a B.C. study where they found that slightly more than 30 of the fish that were bleeding profusley, at the time of release survived. Don't have any idea of waht "bleeding profusley" means, but I think it tells me that many fish that are bleeding will survive.
I do remember they determined "survival" by keeping the fish in a tank for three days. Those that looked to be in good shape at the end of day three were considered survivors. That said, if it was legal to kill and you beleived it wouldl die, keeping it is the right thing to do.