Hey Nyphren! Unfortunately I can't do anything about the previous order in terms of refunds or anything, really sorry you grabbed it twice!
As far as the beta build goes, it's greyed out because I haven't yet pushed anything to that branch. If you download the current demo, that's technically the "beta" as I updated the demo in the new Unity engine for everyone to have access. Once I update the Unity version to have the same content as Twine (all of the Patron stuff) then the beta branch will be updated and the demo will fully replace Twine. That will happen soon, I'm still doing QA to make sure there aren't any bugs.
So for right now grab the demo from the itch page. :) I'm aware of a bug (which I have fixed, but it's not uploaded just yet) on Windows that causes the zip file to give an error, and the itch app won't work either, but the zip file works okay even if it complains.