Sorry we overlooked this! Until an update's released that has better resolution-independent support, you can run the game using command line parameters to force a 16:9 (windowed?) aspect ratio.
(Whenever I do this for something I might use often, I make a shortcut to the executable and the command line parameters to the shortcut's properties.)
e.g. TerraNil.exe -screen-height 1920 -screen-width 1080