Happy to see another musical game in the jam! I love the idea and it could be expanded easily adding new places to perform and obviously more instruments and such.
Gameplay wise, I like how you implemented the instruments and being able to enable and disable them is cool, but I suggest also adding a way to change the volume of each instrument, by the time i had the saxophone it became a bit too strident with everything playing at the same volume. When mixing or producing music, as you add more sounds they boost each other's frequencies so it ends up sounding way too loud if you don't control the volume. Also, being able to close the store and instruments by clicking outside the window would be a huge QOL change, alongside being able to open one menu while the other one is open (either opening both or switching to the one you click without having to close the other first). Also it would be better if clicking didn't have a sound effect, specially being a game about music.
The art is cute but it's inconsistent. I would suggest trying to maintain the same pixel size for all the sprites, menus and background, that would help a lot in making it look better.