If I could go back to being a teenager

I remembered teenage is the most hardest time of life. I didn't know what I am goona do, but I have confidence with no evidence and no skills at all. Teenagers are so mean to others. They don't know how to handle responsibility. It was more easier hanging out with new people when you grow up than when you're teenager. 

I had hard time to make new friends at the new semester in every year. It was so hard and I felt anxious every time. Maybe I spend more time for handling my emotion than doing my things. If I could go back to being a teenager, I would run or walk every day, read Dale Carnegie's book, write essays on my blog, love to use english every day, do more fail, gather people and do something together. 

If I could speak and write in english fluently in my teenage, did I wirte a book in english? What kind of contents I want to say in my book? I always think If I have enough time and money, I will do 'this'. But what is 'THIS' to me?