Dear Past Self (I'm thinking of 17 year old me),
You may think you have everything under control, that you are on a straight and narrow path, that you know what you want and what you need. But the truth of the matter is: you don't. And that's really okay. What seems to be the end of the world right now, you'll look back on and wonder what the fuck the big deal was. Life is going to get messy, you're going to lose control of things, nothing is going to be perfect, and you're going to be okay.
Society is fucked up, and you don't have to follow what society and your classmates deem 'normal', 'beautiful', or 'skinny'. Learn to be happy with yourself for who you are. Once you become confident and comfortable, if you feel the need to change, then great because you're doing it for you and no one else. Change is the only constant thing you can count on. Change is good. Not scary because you have control over who you're changing into. You don't like something about yourself? Change it. Work at it, and don't give up.
Don't settle for anything less than the best. That goes for everything. The people around you, the jobs you take, the things you do, the effort you give. The more you put into something, the better off you will be. Trust people, let them in. Not everyone will hurt you. And if they do, it's okay. It's a learning experience. Don't be afraid to tell people no. Stick up for yourself a little. Let people know what you really want and how you really feel. When you say 'yes' to others, make sure you are not saying 'no' to yourself.
Listen to your heart. Live your life to the fullest. Don't take anything for granted. Be happy. Let the bad roll off your back and show the world who you really are, how happy you really are. You'll love yourself and those around you more because of it.