When I read your letter, I wondered why you wrote it -- and I couldn't help but ask myself if it was because you aren't as confident in your heart as you claim to be. Only you can answer this, of course, but I hope you'll have the courage to ask the question.
Even if you truly believe you don't need God, I pray that you'll reconsider, because some day you're almost certainly going to confront something you can't handle on your own. How will you react when the doctor looks you in the eye and tells you it's cancer? How will you react when someone you love is taken from you? I'm reminded of the Psalmist's words: "God is our refuge and strength, an ever-present help in trouble" (Psalm 46:1).
Most of all, some day you must face death -- and you'll be facing it without hope. This life is not all there is; your body will die, but your soul will live on, and some day you will stand before God to give an account of the way you've lived. The Bible warns, "Man is destined to die once, and after that to face judgment" (Hebrews 9:27).
Don't stay on the road you've been traveling any longer, for it's a dead-end road. Instead, discover the joy and peace and new life God wants to give you, by turning to Jesus Christ and asking Him to come into your heart and life. You'll never regret it.