How do I force a particular resolution?

[HouseLyrander]

The only resolutions this game lets me pick in the options menu are either way too big to fit on my screen **OR** a mere 1280x720, which is really small even for my old monitor. I tried using Steam launch preferences to force a resolution but that did nothing. I also went in to the GameUserSettings.ini file in %LOCALAPPDATA%\GunGraveGore\Saved\Config\WindowsNoEditor and manually changed every listed resolution there to the one I wanted, but when the game reached the main menu it forcibly reset itself to 1280x720. I even tried doing this while my computer was set to a different resolution but the game keeps defaulting back to 1280x720. How do I fix this?

EDIT: If it matters I am running the game in Windowed