How do I stop feeling like i'm ruining my life, even though nothing major has happened? (Just poor grades, no social life at all, and weight issues)

You haven't ruined life. My teacher once told me until you have given up you have not failed. The fact you're seeking help says you have not given up on you. There many paths to success. There are different learning methods to explore to help you study. It took me awhile to find the right one for me. As for social life, do what u love to do always & u will find others who the same thing. There is always time to improve your life.