We as parents spend a lot of time daily making decisions concerning their children. I would be willing to guess that after they make those decisions, they spend at least twice that amount of time doubting themselves.
No one person has all the answers. Sometimes your decisions will be wrong, but probably more often they will be right. To spend time second-guessing yourself and agonizing over the decisions you have made is fruitless. You have done the best you can, now relax.
Parents are not infallible, they can be wrong. Admit when you make a mistake. Kids respect a parent who can apologize and say they were wrong. I believe it opens the doors for them to ask forgiveness when they've made an honest mistake, Of course, we all know that the same problem over and over again is not a mistake, but a bad behavior. That should be handled differently. If your child comes to you and honestly admits he has 'messed up," you should show understanding, as you would want him to show if the situation were reversed.
Once a parenting decision is made, allow it time to see how it works out. Remember that in most cases you, as a parent, are only responsible for your reaction to things. Your teen is responsible for his actions.
Make a decision only after you think about it carefully, say a prayer, and hope that your teen will do the right thing. Once a decision is made, trust in yourself.