Head to the file tallbagel/base/settings.json -- adjust the resolution there and you should be able to make it fit your screen. If the menu buttons are visible on the game start screen you can also navigate to the settings file there.
i found the file, it is un-editable
It's a JSON file, so you'll have to open it in a text editor specifically. If you're on windows, right-click it, choose "open with," and select a text editor like Notepad. (Notepad is better than Microsoft Word here.) Once you get in there, you'll see some lines that look like this:
Change those numbers to the resolution you'd like the game to be. Then save the file. Make sure to retain its .json suffix.