Online resources to check out include Khan Academy (a tried and true way forwards if you have trouble with arithmetic is to do every exercise), PatrickJMT, Paul's Online Math Notes, BetterExplained, and MIT OCW Scholar.
A good way to review precollege math is the Art of Problem Solving contest prep books. It might make sense to work through this alongside the college class. Working through these books and Velleman's How to Prove It should prepare you for Spivak.
You might wish to read this book and Polya. Scott Young's tips can be useful to streamline your learning.