CS or PoliSci? CompSci is one of the most competitive programs to win acceptance at a strong program, and it is one of the most demanding academically. PoliSci is far less competitive and demanding. AOs for these programs will be looking for very different academic credentials when evaluating applicants. If you are serious about CS, you will need STEM APs, including Calc, with good scores. You will also need a very strong SAT Math score (CMU’s 25th and 75th percentile math scores for CompSci students are… wait for it… 800 and 800). My guess is AOs for politial science will be looking for AP History, Econ, etc., and strong writing skills.
Think about which path you want to pursue. Your decision will drive what classes you take in your junior and senior years, and what ECs you do.