My first reaction is that you are doing very well.
My second reaction is based on this comment:
Do you know what your budget is for university? Do you know what your budget is without taking on debt? Do you have siblings who are also likely to be attending university?
Have you or your parents run the NPC for CMU? To run the NPC, you will need enough information about your parent’s finances that they will probably be better off just doing it themselves. If your parents are divorced or separated or own a small business or rental property then the NPC is likely to be inaccurate and too optimistic. Otherwise it is likely to be relatively accurate.
There are a lot of universities that are very good for various sciences and for math. Graduates from top schools (such as CMU or MIT) will regularly and entirely normally find themselves working alongside graduates from a long list of other universities and no one cares where anyone got their degree (okay, I once vaguely knew one person who cared, but he was annoying). Top graduate programs in various sub-fields of science or math will typically have students who came from a very, very wide range of undergraduate schools. Thus you really should be able to find a university that is very good and that is affordable. Whether it will be called CMU or MIT is harder to say, but really doesn’t matter.
I think that you are competitive for CMU, but it is a reach and I would be surprised if your chances are any better than the overall acceptance rate, and your chances might be slightly lower than the overall acceptance rate. Since you also mention MIT in your post I will guess that with a ranking in your high school class of 25th out of 545 students, your chances at MIT would be lower than the overall acceptance rate.
We will be in better position to guess at your chances a year from now and after you have actual SAT results and another year of grades.
In terms of recommendations regarding ECs, my suggestion is that you do what is right for you, and do it well. This is also my interpretation of the advice given on the “applying sideways” blog on the MIT admissions web site which is worth reading (a quick Google search should find it). This notion of “do what is right for you and do it well” is what my immediate family had done and it has worked out for us. However it has led us to 8 different universities (one each for a bachelor’s degree, and a different one each for graduate programs).
And I will leave with one other recommendation: Think about what you want in a university, and look for a school that is affordable and that is a good fit for you. Ranking mostly does not matter. A good fit does matter. As one example MIT is likely to be a LOT of work. The desire to work that hard should come from inside yourself if you are going to go there. As another example, think about whether you want to be in a big city or a small town, and how large a school you would like to attend. Visiting a few schools can help you get a sense of where you might be more comfortable. It is worth the time and effort to think about what a good fit for you is likely to be.