that small of a mat would be good for taking to a class or to use for small squares, squaring up small blocks by your sewing machine ect. you of course can fold your fabric or layer it and cut multiple squares at once (with a sharp blade in my cutter i cut up to 4 layers at a time, i have a friend who cuts 8 layers at once but i loose accuracy with that many)
so, at some point you will be wanting a larger mat but you can certainly make do with what you have, using a smaller ruler (to match the smaller mat) will make it easier too, it is hard when your ruler is larger than your cutting mat.