If you have taken 3 writing classes/semester, have you been able to also take the other 4 cores (math, foreign language, social studies and science) all four years?
For your reach schools, it will be very important that you can show aptitude in all core subject areas, not only English-related ones.
As others have said, your school’s college counselor will give you the best idea of your chances. Especially at a private boarding school, he or she will understand the specifics of how your application compares to others from your school, how it compares to others who have been accepted from your high school, how your personal story will be meaningful to AOs, the relationship between your high school and a given college, etc. Even if you provided us with all of that personal and specific information, no one here will know better than your high school counselor.