Is it wrong to cite a source I did not use?
Ask yourself: why did the Professor put this requirement?

It is almost certainly not just to make your life difficult.

A more likely explanation is that your professor wants you to not only provide your own analysis, but to back your analysis up with others' research and analysis.

So if you were to cite a source without using it, your mark won't likely go up, because your arguments are no better supported. Any good marker will see this. So if you're trying to increase your grade, you should add a source, and incorporate it into your arguments. In any case, I suspect your paper needs work to meet your professor's expectations.