The fact that you took a creature into your home and heart that the vast majority of people would reject on sight says a great deal about you. The fact that you're torn up about the passing of the snake says something good as well. The important thing to remember is, like Harm286 said, everything happens for a reason. You're a good person who tried to do what you could. Even the greatest surgeons lose a patient now and then and they've had years of specialized training. It sounds to me as if you were just in the right place at the right time to offer a little comfort to a snake that would have otherwise passed alone in the shop.