Basically your Grandmother has parented you for 13 years. It would be surprising if you remembered your Mother other than through shared stories and pictures. Thank goodness your Grandmother was able and willing to care for you all of these years.
You mentioned that you have "messed up your life since they left you." Typically young children do not consciously mess up their lives. That does change as you get older because you are better able to make your own choices. Even if you had been guided by your parents for the past 13 years, you may still have made choices that "messed up your life."
Unfortunately we cannot re-wind our past and choose things that are better for us. We can however, begin right now, today, making better choices. If you need help to do that, talk with your Grandmother, a teacher or school counselor and they will help you.
Good luck and let us know if there is anything else we can do to help you move forward in a positive way.
Pat, Counselor