I encourage you to make use of the midterm retest option, whatever your midterm grade. You can add up to 20 points to your in-class grade, and that can make a difference in your overall score. It can only help you.
As I mentioned in class, the retest is short (approximately 3-5 questions). The questions are taken from the in-class exam itself, so you should use it to study. The questions are of the fill-in-the-blank variety; no essay questions are on the retest.
There isn't an official, in-class time for the retest. You can scehedule a time for your retest by contacting me through jtirrell@purdue.edu. I would prefer to use my office hours for this (after our class until 4:00), but I will work with you to find a time that is acceptable to both of us.