You should be able to change this in the setting, but I'm guessing you're not able to access them...
If you go to "C:\Users\XXX\AppData\Local\BE_Witches", where XXX is your username, you should see the "settings.ini" file. Open it with a text editor, and make sure fullscreen is set to "1.000000", then launch the game
If this doesn't work / is already how it was set, try changing
fullscreen="1.000000" to fullscreen="0.000000"
and make sure that resolutionID="0.000000"
Save, then launch the game. This should make the game appear in a 1280x720 window
Hops this works! If not, could you let me know what resolution your screen is?