Your notebook looks functional and useful, but pretty simple, based on the pictures on your website. There's nothing wrong with that (and if I composed music, I would probably order a copy), but it doesn't necessarily attract the eye.
You might want to consider an edition that has little things a musician might find interesting or useful included in it. That seems to be how these planner people attract people, is a lot of little things that people probably don't really need but enjoy filling out anyway (the link says they compiled all sorts of stuff into their planner, and for anecdata my fiancee is a huge planner nut and loves checking out planners with all sorts of different approaches to layouts and fields and organization and whatnot).
For example (and I don't recommend going this far necessarily, but it might inspire you), a board game designer decided to design a playtesting journal for other board game designers, and threw all sorts of little things in there, like a built in scoreboard, a die number on the page so it could be opened to a random page to simulate a die roll, added achievements with a sticker page, lots of fields to remind the designer to ask certain questions at the end of the playtest, a game contract checklist, a page with guidelines of sizes for various components for getting the game printed by a manufacturer, etc. He did a Kickstarter for it and raised $30k for it (not as much as the article, but still not bad). I backed it and got a few for myself, even though I've kind of settled on my own method for playtesting games, I'll give his a try.
Anyway, his journal serves a specific niche like yours does, so maybe something in there will inspire you to find ways to make your notebook stand out and attract more people to purchase it.
https://www.kickstarter.com/projects/828934174/fail-faster-t...