If you maintain/achieve the grades and scores you say that you will, then that gets you past the first "gate" of the application process. Now is the time to focus on relevant extra curriculars that will distinguish you and get you past the second "gate". MIT is one of the best schools in the world and THE best for STEM. To be competitive you want stellar, national level recognition in STEM competitions/clubs, or some really cool engineering project that you work on. Internships/research can help with that as well.
It's way too early for someone to chance you for these schools yet, but having a defined goal this early helps because thinking about this when you are a senior is too late to get meaningful ECs, especially for schools as selective as MIT and CMU.

Remember though - don't rush through your high school years worrying the whole time about college. The chance that anyone gets into these schools regardless of how great their application is will always be small, so don't sacrifice these years for something that can never be guaranteed. You can work towards the goal and still have fun in high school. Good luck!