Same, I played the preview and paid for what is called Donation Version....I don't understand why the option even exists yet, but I am NOT happy about it. The file I paid for is NOT labeled "preview", seems like a quick way to get peoples money.
Those files should NOT be there when you're actually paying for the free demo.
Understand I release builds linearly to make development easier. After nearly two years I did a public release on New Years eve.
Since then i've been moving on to developing the non-preview version of the game, and this is taking some time. Some builds have been released, but only to monthly supporters because it's extremely unstable. But once the build is more stable you will see it released here at no additional cost.
This also includes all future versions of the game even when i intend to increase the price.
I'm sorry it's taking so long but part of it is additional planning needed, i will do a news update soon to clear things up since this seems to be a point of confusion for people.