Yes, God has a plan for our lives–but He also gives us the freedom to reject it or ignore it. When we do, however, we pay a price–as I'm afraid you are discovering.
You may have turned your back on God, but listen: He has not turned His back on you. That doesn't mean He likes what you've done or pretends that it didn't happen–but it does mean that He loves you, and that He wants to forgive you and put your feet on a different path. No matter what you've done, nothing is too great for God to forgive. The Bible says, "Blessed is he whose transgressions are forgiven, whose sins are covered" (Psalm 32:1).
But God not only wants to forgive you, He also wants to give you hope for the future. No, you can't change the past and you can't undo the wrong you have done. But with God's help you can change the future! The Psalmist's experience can become yours: "You have made known to me the path of life; you will fill me with joy in your presence, with eternal pleasures at your right hand" (Psalm 16:11).
How can this happen? Start by turning to God and confessing your sins to Him, and then asking Christ to come into your heart. Then ask Him to help you live for Him every day. You can begin again, by giving your life to Jesus Christ and depending on Him every day.