texas*princess...
I teach English at a large University. I hear excuses for poor grades ALL the time, and I know that I, unfortunately, have developed an automatic BAD reaction to these excuses...no matter how valid they may be. My advice is simply to allow Tuesday's appointment to be strictly about you, your grade, your commitment to preparing for the exam, and your understanding of the course material. Afterall, you made the appointment before you knew about the cheating. The professor should be made aware of the cheating, so I strongly recommend an anonymous report to the professor or to the appropriate dean. An anonymous report only has the potential to HELP YOU. A direct accusation in the midst of your meeting has a strong potential to HURT YOU.
However...here is another perspective. I asked my husband (who teaches English at the same school) what he would do in this situation. He said that he would consider your accusation, and if there was real evidence of the academic dishonesty that you described, he would give those students who cheated a failing grade. Your grade might improve slightly, but there is always the possibility that the cheaters did not have the very best grades on the exam. You grade might not be affected at all. My hubby said that he would not feel that you were making excuses.
Two sides of the issue...take them for what they're worth
Good luck!
LM