I have a spinning wheel in GarageBand on my iMac

I have a spinning wheel in GarageBand and it won't allow me to click on preferences or anything. I was just about to start editing a drum track in MIDI. I don't know what I clicked on to set the wheel in motion, but the mouse now does nothing more than move the spinning color wheel around on the screen. I am new to Apple, so I don't know how to overcome this or safely execute a hard stop. I've just started the project, so it will be no great loss if I'm unable to save it.

[Re-Titled by Moderator]