Being a Christian means that you have a personal relationship with Jesus Christ, that He is your Savior. You must know Him for yourself. You can say a prayer something like this:
"Jesus, I know that I have sinned against you. I know the truth is that I have sinned by my own choice, and I am the one responsible for it. I know that I have earned punishment from You, and that the fair punishment would be death. Jesus, I believe that You died in my place. Forgive me for my sin. I cannot cover or take my sin away, I am relying totally and only on You. You are the only one who can save me. I reject my sin, I turn away from it, I repent. Come into my life, take away my sin, and show me how to live my life in a way that is right and pleasing to You."
If you have prayed this, YOU ARE SAVED! You are now completely forgiven, a new creation, innocent in the eyes of God. Welcome to the family of God!