Try checking if the lock turns completely with the door open. If it works then the bolt might not be getting past the strike plate on the jamb. Look between the door and the frame when closed and see if the lock is hitting the strike plate. You can also see if pulling in on the door more than normal gets the lock to work. If it does then it is hitting the strike plate. Up north with swelling from the winter and shrinking in the summer it is common to have two sets of holes (one for each season) for the strike plate. Reposition the strike plate in the direction you think it needs. If it does not work properly while the door is open then the bolt is misaligned or you have an internal problem. But more than likely since this is a kwikset it is your strike plate.