University Studies and a question for CS/SE/all-those-things people

I'm applying to RIT undeclared (university studies), but can someone tell me more about this? More specifically, can I choose what I want to explore AFTER being admitted, or do I have to still apply to specific things? HOW DO I EVEN DECIDE ON TWO THINGS TO EXPLORE I CAN'T HANDLE THE VARIETY

Also, I'm considering going for CS or SE, but I hear those things are pretty math intensive (not as much as, like, CE though, I know). I have done all my required math credits up to pre-calc, and was supposed to do calc this senior year but decided not to. How screwed would I be?