No sin is too big for God to forgive, and the reason is because every sin we have ever committed—every one, without exception—was placed on Christ when He died on the cross for us. Jesus didn't die just for our small sins; He died for all of them! The Bible says, "He forgave us all our sins" (Colossians 2:13).
This is why I invite you to turn your life over to Christ, by repenting of your sins and trusting Him alone for your salvation. If you have never done so (or if you are uncertain if you have done so) pause right now and ask Him to forgive you and cleanse you from all your sins—and He will. God's promise is for you: "If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness" (1 John 1:9).
But I believe God wants you to take another step—and that is to seek the forgiveness of those you have hurt. This won't be easy, and some of them may reject you when you tell them you are sorry for what you did, but you still need to take that step. Not only will it help cleanse your own heart and mind, but it will show others the transforming power of Christ in your life.
Then make it your goal to live for Christ every day. No matter what our past has been, the future will be different when we learn to walk with Him.