Adolescent period is stormy and at times can lead to heart aches.. and disappointments. What you seem to have is infatuation towards her and also seem to be more in love with the idea of being in love. Please direct your energy towards other things which you may enjoy - learn a new skill or musical instrument or work towards a social cause which helps you boost your confidence. Give the girl some time to decide and take it easy ! Not everything that we want comes to us at all times. Everything comes to man but one must wait. Do not think negatively about yourself just because she said no . Life is beautiful ! Just open your mind for a different view ! All the best !