I think some song titles in the book would help it look finished. I would be scared I would mess it up too since it is so small. Maybe you could type up a song or two on the computer and print it off small and cut the paper the size of the book and lay it on top of the book on your cake. It may not be edible but it could always be taken off later! HTH
Maybe even just a few black gumpaste/fondant musical notes (cutouts) floating over the cake, or laid out on the board?
I would definitely write a song title or add some music notes to the open book. You can practice on a scrape piece of fondant before actually doing it.
I agree, throw some musical notes on the white sheets.