Feb. 7, 2021
Here's the answer to a similar question that “The Dean" received earlier this fall. However, your situation is a bit different because you've already received your early verdict from your top-choice college and, above all, it's later in the semester now so you will have little time to bring up your grade.
Nonetheless, you should follow the suggestions included above. Talk to your teacher right away and ask if there's anything you can do, such as an extra-credit project, to boost your grade to at least a C. (C's sound far less heinous to admission folks than D's do.) Even with just days left in the term, you should go to extra-help sessions, if offered, and engage a tutor if you still have an exam (or any other tests) looming. Not only will these measures potentially improve your grade a notch, but they will also provide material for the report you will need to send to your college.
You should write to your regional admissions rep today (that's the staff member who oversees applicants from your high school) and warn him or her of your pending bad news. List any steps you've taken to stay afloat in the class. (Perhaps you've already tried extra-help sessions and professional or peer tutoring?) You must ask if your Early Decision acceptance is in jeopardy of being revoked so that you'll have time to submit other applications, if necessary.
The retake of the SAT, however, is a colossal waste of time. Even a perfect SAT score won't offset a low grade. What's important, instead, is to convince the admission committee that you are struggling in AP Physics but not slacking. If your teacher can corroborate your efforts, it will work in your favor. And if your grades in your other classes (especially the most rigorous ones) are as good — or better — than past grades, that will help your cause, too.
Since hindsight is 20-20, you've probably already figured out that you should have jumped on this problem sooner. So don't be an ostrich this time. If admission officials see that you care about your grades, they are apt to be more forgiving than if they suspect that you've just been goofing off and counting the days till graduation.
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