When Do Colleges Rescind Acceptances?

@Sally_Rubenstone,
First of all, thank you! That’s good news to hear.
In order to answer your question, things start getting a little complicated. First, I’d like to preface with the fact that IB Math HL is incredibly difficult, even for me. The reason my grade was so low is that the only grades we’ll have for the term are 5 point homework assignments (about 8 of them), 15 points for initial research on our IAs, and 1 100 point exam. You probably could infer that the exam was the deal-breaker for me. Our teacher used only questions off of old IB tests, and gave us limited time to take the exam. Two others in my class who were also previously strong in math did much worse than me on this test (Once curved, I got an 83), and the highest raw score on this test was a low C. To make matters worse, the teacher curved the test based off of each other, not based off an IB test curve (as other teachers who make their tests out of old IB test questions do, so as to prevent their students from failing). She decided that the average grade would be equivalent to an 80%, and to curve us off of that. As the class (at the time, two people have dropped) had 5 people, this made the pressure to do better than one another very intense. In addition, the top two scorers on the test (I was the middle) both could be considered “math geniuses,” and would be taking college level math classes (Calculus 3 and above) if they did not need an IB math class to get their IB diplomas. Again, this made it incredibly hard for the other three of us, who only had taken IB Math SL (which offers a much more limited instruction in calculus), to compete. Things get even more complex when you factor in that the weekend before the test was homecoming weekend and the Friday was our school spirit day, meaning time to study was already limited. But, that’s not the important part. The night before the spirit day, 8 of us slept over at a friends house. One other girl and I took our stuff to school, and thus didn’t have to return to our friends house, the other 6, when they returned after school, found that the mother of the friend whose house it was had passed away very unexpectedly. This meant a lot of the weekend was devoted to giving emotional support to this friend, trying to rearrange plans for homecoming, etc. The only thing is, most of the friend group is a lot closer to this friend than I was, so they were much more involved with grieving process. I’ve considered including this as an explanation for the B (as colleges always say things along the lines of “If there’s a significant drop in your grades, tell us why, and we’ll likely understand”), as my time to study and overall mental state were definitely affected by this sad event. However, as of right now, I’ve decided not to because: 1. I’d feel terrible trying to use someone else’s mom passing away as an excuse, and 2. Since the grade is not that low, I wouldn’t want Dartmouth to think I was making superficial excuses to try to cover my poor performance.
Do you think I should stay the course, and leave the grade unexplained, or tell Dartmouth of the events the weekend before the test?
Thank you again