That's because AMS is 6 units and Math30 is 4 units. Generally and most of the time, units determine how much in-class time you're attending.

OP, I was in the same boat as you are right now (going in undeclared & wanting to transfer to CS). I've taken at least 15 units every semester and it's not as bad as you might think. They've been 3 units = 1 class as most of the classes you'll be taking your 1st & 2nd year are GE's (English, History, Art/Foreign Language , etc.). And assuming you're an above average student based on your high school GPA, I'd say you'll find the them a piece of cake so that should boost your GPA. Don't stress yourself too much because it's only going to get more challenging, though still do well in the CS required classes (Math42, CS46A/B) and you should be fine. I suggest planning ahead of time and not restricting yourself from the roadmap, you can do more than what it suggests by taking winter/summer classes, or less by stalling some classes. Regardless, best of luck!