Chances at Berkshire, Choate, Andover, Exeter?

Hello folks!
I am a Brazilian student, who is currently attending a Boarding School in Canada on a full scholarship due academics. I am applying for grade 11th as a repeater at the following schools: Choate, Berkshire, Andover, and Exeter.
I rather took the SAT than the SSATs, in which my score was not so good (a 75% overall average); But my curriculum is quite interesting.
I have a gold medal at the International Math Olympiad Without Boarders. (A french math Olympiad)
Gold Medal at Mathematical Kangaroo as well as some medals at national level Olympiads, such as Math, Geography, Physics, and History.
A good background with social changes activities, including my own two volunteer projects (on the educational and environmental fields), MUN at college and national world level, and now part of the Brazilian Delegation at the Youth Assembly at the Headquarters of the United Nations in New York.
Head of Essay at the school newspaper, captain of Volleyball team and soccer player for seven years with an overall academic average of 97%, and with a perfect grade 9th transcript with an overall average of 100% (A+). Before coming to Canada, I was in one of the best High Schools in my country, also on a full scholarship.
What are my chances at these schools (Specially at Berkshire) ?

***Background/Language
I am from a low-income family, everything I have done so far I did by myself and with help of sponsors, making online crowdfunding and working on part-time jobs to raise the money to pursue on my dreams.

If you require a large amount of aid, you’re chances are incredibly low for Choate/A/E as an international 11th grade applicant. You’re SAT score also needs to be raised.

Also, what is the International Math Olympiad without Boarders? At first I thought it was IMO, (of which I was thinking why not just apply straight to MIT?)

@babymalcolm is a French Math Olympiad in which not only you, but your whole class participates. It is way further than only math knowledge, but also organization and leadership skills.
And by the way, I have a brazilian friend who is in a full scholarship at Exeter, and I also taught that they were generous when talking about aid.

Do you have any AMC/AIME/USAMO scores? These will hold more ‘bulk’ than a competition like Math Kangaroo. I believe Canadians are eligible to participate.

On a more serious note, since you are already at boarding school, and in 11th grade, wouldn’t it just make more sense to wait a year and apply straight to college? 11th grade is a very difficult year to adjust, both academically and socially.

Have you considered United World Colleges?

@CaliMex Yes, I have. But since I am in Canada I cannot apply through their boarding committee.
@babymalcolm Ok, sorry I did not explain, let me point. The school where I am now, in my conception, is not a good environment to learn and for sure it is holding me to achieve my future goals. I am sure that being a student at an American Boarding School will contribute a lot to my future in general. There I will be able to receive much more guidance through my University`s path along with the experience of being already inserted into the American educational system.
One more thing, my strength is not in Math, I just do and get good results. I am planning to do Political Science and this event at the United Nations Headquarter for sure will count as a good experience on my application.

I’m a student at Berkshire so feel free to pm with any questions!