Everyone has times when they wish they could turn back time and erase a mistake they made. Well, the good news is that you can! God gives you that opportunity and that chance. He says,
"Come now, and let us reason together,' Says the LORD, 'Though your sins are like scarlet, They shall be as white as snow; Though they are red like crimson, They shall be as wool.'" (Isaiah 1:18) That means if you tell God you're genuinely really, really sorry, repent of your sins, and ask forgiveness, He blots them out and it's as if they never happened! You could be the most horrible person on earth, but if you genuinely ask God's forgiveness and turn your life around you truly are a new person in Christ, including the washing away of past sins! It is by the grace of God you are forgiven. So, don't despair if you keep on making mistakes...no one is perfect. Just try to learn from them, do better in the future, and genuinely ask God to forgive you!