You're right: It isn't enough for us simply to be sorry because we've done wrong. Judas was very sorry because he betrayed Jesus; the Bible says he "was seized with remorse" (Matthew 27:3). But it wasn't enough, and in spite of his remorse, Jesus said Judas was "doomed to destruction" (John 17:12). He ended up committing suicide.
You see, something needs to be added to our sorrow for our sins and that is repentance. To repent means to turn from something or to change our attitude about it and when we truly repent of our sins, we turn from them (with God's help) and change our attitude toward them. Jesus' first recorded sermon begins with these words: "Repent, for the kingdom of heaven is near" (Matthew 4:17).
But something else needs to be added to our repentance and that is faith in Jesus Christ and what He did for us. Jesus was without sin, but on the cross all our sins were placed on Him, and He took the judgment we deserved. He did for us what we could never do for ourselves, and because of Him we can be forgiven.
The most important decision you'll ever make is what you will do with Jesus. Will you ignore Him or will you turn from your sins and trust Him alone for your salvation? God loves you; He loves you so much that He sent His only Son into the world to die for you. By faith turn your life over to Him today.