Think for yourself, but don't think that you are infallible. I espoused a bunch of nonsense when I was younger, and believed that I believed them. In fact, I told my mother a few years ago that I was issuing a blanket retraction for everything I said from about age 16-25.
Also consider your actions carefully - some mistakes/choices can never been undone, the damage can never be repaired. Trust me, the bitterness of regret, when you know it's absolutely your own fault that you hurt yourself and other people, and nothing can change it, is something I wouldn't wish on my worst enemy. You can resolve to be a better person and even, through prayer, the sacramental life, asceticism and acts of charity, become one, but you can't change your past.