Soon to be computer science major with some questions
Firstly, is CS going to be Math heavy?
It's not a very easy question to answer as it depends on quite a few factors. How good are you in Mathematics and how strong are you with the basic concepts? If you were comfortable with the Math you have done so far, then you won't have any problem. If not, then there is nothing that some hard work cannot solve. Plus CS is definitely not he most heavy of all the majors in engineering or sciences. I believe Mechanical, Aeronautical, etc to involve a lot more advanced Math in them.

Secondly, what will you be learning?

You will be learning Algorithms, various programming languages and there pros and cons, maybe artificial intelligence, operating systems, networking, database theory, some electronics I believe, and maybe sensor networks,etc.

Thirdly, should you quit stressing?

Definitely Yes. If you have decided to become a Computer Science major then I am guessing that you have interest in the field. If that is true you should be able to grasp the concepts just fine.

My Advice, pick an area like Artificial Intelligence or Networking or Operating System etc, which ever field you like best, early, and try and master that field. That will help you tons in the future.

I have a PhD in CS and seen quite a few young guys go through the same phase as you. It's very natural to feel nervous about the unknown, specially when it's about your career and the rest of your life. Just try and make smart decisions whenever you have to. Plus, there will be lots of people around to help you when you are unsure.

So, Good Luck and have Fun.