You are currently an 8th grader. Please please take the time to enjoy your high school years without feeling the need to be competitive for those tippy top three schools.
There are a LOT of good CS programs in this country, and many are not as competitive as the three you mentioned where acceptance rates are VERY low.
In addition to accelerated math, you also need excellent grades in your other HS courses, and for colleges that require the SAT or ACT a great score on that.
And you need to have a life!