When you get to the final results screen where you're graded for your score, tap the tab button until the question mark button is highlighted, it'll then bring up a pop up screen with more buttons. With the tab having still selected the question mark, click on the "Useless" button to increase your score by however much you want. As far as I know, there are no limits as to how high you can raise your score. You could go up to a thousand for all I know, but for all I care, I won't waste my time trying.