This is in the spirit of passing on some of the responsibility back to the students (radical, I know).
Now. Stop for a minute. Breathe. Consider the entire semester. Consider what kind of learner you were/are/have become. Consider how much time you spent thinking about the material in this class. Consider the effort you put forth in thinking about and learning the class materials. Consider your innate ability/intelligence/smarts. Consider the grades that you have received so far. And finally, consider the degree to which you improved over the semester (from your perspective as well as mine) in terms of how much microeconomics you grasp. Now, give yourself a letter grade and justify it in three (3) sentences.