I hope you got this working, but there are a few things you can do. If you intend to print through the driver, then the ZPL driver is more useful. The first thing to do is calibrate the media. The setting to do that is in the driver, under Printing Preferences -> Tools -> Action -> Calibrate Media.
After that, you want to use the Options and Advanced Setup tabs to set up the media settings. Make sure the "Use printer settings" box is not checked if you want to have the driver set everything including print width there.
The printer has no sensor to detect the media width, only the length, so you have to set it.