No, it's not too late for you to turn to God -- and I pray you will, because very shortly you will enter eternity, and you're not prepared for that day. The Bible says, "Now is the time of God's favor, now is the day of salvation" (2 Corinthians 6:2).
One of the Bible's greatest truths is that God loves us, and no matter what we have done, He yearns for us to turn to Him for the forgiveness we need. Yes, it would have been better if you'd lived an honest life and had given your life to Christ many years ago. Perhaps your letter will be a warning to someone who is tempted to go down the path you followed.
You can't change the past; you can only regret it. But you can change the future by giving your life to Christ and discovering the joy of His forgiveness. By a simple prayer of faith ask Him to come into your life to forgive and cleanse you -- and He will. May your prayer be that of King David: "Wash away all my iniquity and cleanse me from my sin.... and I will be whiter than snow" (Psalm 51:2,7).
I also urge you to do whatever you can to repay those you've hurt. It may not always be possible -- but even a word of contrition will let them know you regret what you did, and may even point them to the Savior who has changed your life.