When you say 'stretch' - have you used the settings in the CFG file (opens with Notepad)? Underneath the required entries in the [video] section:
[video]
windowed = 1 # windowed mode
borderless_window = 1 # no borders around window
battle_resolution = 1920 1080 # set this to your actual desktop resolution
campaign_resolution = 1920 1080 # set this to your actual desktop resolution