I don't think you did it wrong, I think you scrambled the brain, so I doubt there was any brain to feel pain. I think your problem was you had the misconception that pithing kills them. The whole idea of it is to scramble the brain but leave the heart beating so it will pump all the blood out.
Sorry you had this experience, but I wouldn't give up; sounds like you had it right.
Sorry you had this experience, but I wouldn't give up; sounds like you had it right.