I'm not sure if this can be done on the MAC version (I'm a PC user), but you might want to try and edit the "config.ini" file in the directory where you have the game installed (it is in the same folder where the ".exe" to launch the game is found). I also suggest making a backup copy as well so you can always revert back to the original if something happens to go wrong.
You can use any text-based editor (I just use Windows Notepad) to edit the file.
UPDATE: To find the "config.ini" on a MAC OS, refer to this quote:
When editing the "config.ini" file, it should look something like this:
The above contents in the spoiler are my own "config.ini" settings, so they are probably going to be different from what you will initially see when you edit your own. But basically the 2 lines I suggest editing are the following:
FULLSCREEN = no
RESOLUTION = 1600x900
First one should be self-explanatory (FULLSCREEN = yes or no). I personally like running in a windowed mode since I usually have more than one application open at a time and I'm not currently rocking a dual (or more) monitor setup. But obviously this option is up to personal preference.
Second one (which is probably the one that will help with your problem the most) is what desktop resolution you want the game to render in. Maybe for some reason the game's default was not optimal for your system, so try changing the value here to a resolution you know that your system supports.
After you're done editing the "config.ini" file, simply save it and then re-launch the game to see if it fixes the problem.