Unfortunately, I've had to end support for Mac versions as I no longer have a Mac to develop on. I'm not sure whether the problem is a 32-bit/64-bit thing, or just because the game was built against a very old version of OS X. On other storefronts, the game is no longer listed as being available for Mac; on itch, I don't have a way to do that without entirely removing the old download. (Maybe I should do that.)
If you need a refund, let me know and I'll try to figure out how to do it.