We've fixed the issue. If you re-download the game, you should be able to switch to full-screen. You'll need to switch to borderless fullscreen from the config menu, as it will still have a border if you do so using the "maximize" button. Please let us know if you have any issues.
As you've probably noticed from following our dev logs, we've been juggling a lot of plates lately and we've ended up neglecting some of our previous releases a bit.
Sorry for the trouble, and thanks for taking an interest in the game in the first place. We hope this fixes any bumps in the road you've run into.