My school offers a double math program Freshman year, in which one can take both Geometry and Algebra II the same year. This places a student in Pre-Calc trig sophomore year, AP Calc AB junior year, and AP Calc BC Senior year.
However, I was advised not to take this double math program, which I’ve realized was a mistake. Senior Year I only will be in AP Calc AB. My question is: how much will this hurt my chances at a higher level school? My absolute dream School is Upenn, SEAS, for computer science, but I already know my chances there are slim(perfect GPA and 1500 SAT, but white well rounded male). Will I even have a chance, or will I be rejected because computer science is mostly math?
None; no college requires BC. Now if there are other applicants from your HS applying to the same college, they may be at an advantage, but there’s no way to say for sure, as Penn, and colleges of that tier, evaluate each application holistically
If you take Calc AB as a class in high school, you still should be able to register to take the Calc BC AP test. You would have to study the additional material on your own. I would check with your school first to see whether they require you take the Calc AB AP test. For many students calculus will be the hardest high school class they ever take, so make sure you are prepared for the work load whatever path you take.