I got a 1540 but a 6/6/6 on the essay
I am looking at the most prestigious of schools
Should I retake it to improve my essay score? or is this one “good enough”?
You shouldn’t retake just to improve the essay score. Your score is good enough. You should focus on other aspects of your application. That would give you much higher benefits than a slight increase in essay score.
Believe me, your targeted schools would care a lot more about other parts of your application, given your already excellent SAT mark.