If I were you, and this answer is only based on your answer… take the time to improve your English. At any American boarding school, the emphasis is placed on reading and writing, and even kids who are native English speakers struggle with this. With that said, a bit of advice we received straight from the head of admissions at Exeter: spend time on the free written response on the SSAT. To boarding schools, this is the most important piece of writing in your application because it’s the only writing that you did not receive help on. It is a true reflection of your ability. According to him, this can make or break an application.
Also, look through this forum to see the stats of other international kids from your country, their test scores, ECs, etc. It will give you a gauge as to what you should aim for and may give you some volunteering ideas. It does not have to be a specific program, you could help old ladies across the street, help carry their food home from the market, or help a kid who’s not at your international school with their homework. Then have someone take a picture of you doing this 2-3 days/week for X hours/day… something as simple as that. ‘Help your neighbor’ as we in the USA say. Just be a nice helpful person. Good luck!