I'm assuming you see a pediatrician or adolescent physician yearly for a school check up so why not call, make an appt. and bring the area to his or her attention ASAP.  If you are still worried - ask for a dermatology referral and let your parents know how concerned you are.  I know that feeling of "why did I ignore it for so long and what should I do now" - so rahter than obsess about it - get it looked at by a professional.  If you are not already - start using a UVA/UVB broad spectrum sunblock that is sweat proof - and re-apply it according to the directions - every day you are outside - on face and body.  If you want a glow - get it from a self tanner - that decision alone can save your life.