GarageBand: Can't extend drum loops beyond 32-46 measures

I started a new project in Garage Band with a drummer track. I want to record other tracks after I have the drum track, but I can't get the drum track to extend beyond 32 measures (or 46 measures in another project). My song is going to be longer than that, of course, but I don't want to record unless the whole drum track is laid down. Or at least, that's how I assume I need to do it.

See attached screenshot where hovering reveals the arrow, but it still won't let me extend it.