There's no more photographic paper, just what is already in the box. Are you timing your paper dippings by a watch or clock? You need to be precise with the timings here. Also double check that your tray solutions are correct.

Perhaps go back to a save game before the photo puzzle and replay, making sure that you turn the main light off before opening the photographic paper box.
Make sure that you listen to the wax recordings all the way through.
Keep us posted.