The backpack will work with RGB LCDs (but wont control the RGB backlight, you can do that seperately from the LCD control) and it won't work with 40x4 LCDs because they have a second Enable pin.
As long as your LCD has a HD44780 driver chip, you're OK. The extra two pins are for the backlight. Your LCD doesn't have a backlight.
We'll show you which holes to ignore in the Assembly section of this guide.