Schitzophrenic

Hi! I wanted to evolve my Dratini on lvl 99 but when i clicked on "yes" nothing happened....now i've got a lvl 100 Dragonair what is really annoying! Is there any possibility to evolve this to a Dragonite? Or maybe to level it down to lvl 99 again? I am really frustrated! Greetings, Schitzophrenic