This world is the place where Allah sent us to become complete Human it means no one ( other that Masumeen (a.s)) is complete and perfect at his /her birth. Therefore if anyone has done mistakes in his /her life as long as he/she is alive the door or Tauba ( forgiveness) is open for him/her. So no need to be worry about your past just ask Allah (swt) with sincerely and with pure heart his forgiveness and then Rely on Him and have solid faith in Him and try not to repeat your mistakes again ( that is the real Tauba). Then nothing to do else.