If you are an atheist, or agnostic, and you die and discover there really is an afterlife, really is a God, do you suppose you're going to hell?

Let’s assume you’ve lived a good life. You’ve helped others. You’ve kept your promises, you’ve never murdered someone or abused a child. From deep in your heart you’ve honestly been a kind, dependable, compassionate, generous, honest, loving person. In short, you’ve been everything a Christian is “supposed” to be, but you acted that way because it was the right way to behave, not because someone is threatening you with hell.

However, you never acknowledged God, never prayed to him for help, or asked him to heap coal fire on your enemies. In fact, you’ve denied his existence to those who asked.

Is that grounds for being sent to hell? If so, why?