If your teacher fails you, this is when you find other solutions rather than passively accept your fate. As others noted, there’s tutors, books, etc., but there’s also plenty of free options. If you had Googled “how to write a great a great ap language and composition essay” you would have found pages and pages of results with websites, blogs and videos (depending on your learning preference) offering concrete tips about how to structure and write the essays. Some paid, but many free. There’s also a pretty active discussion on Reddit. Obviously its too late this time, but its more of a life lesson. A lot of times you will need to be scrappy and proactive to achieve your goals. Life will more often throw up roadblocks instead of helpful mentors or people who tell you how to do something.
Anyway, again, this is not worth stressing about. A 3 on AP Lang is not going to affect your admissions anywhere. Your odds of getting into a T20 are low because they are low for everyone, regardless of your test scores. A single AP score will not make-or-break it. But there’s also a ton of places you are almost guaranteed to get into that are not in upstate NY.