The 3-day right to cancel is generally a state law and I have no idea if it's the law in CA or not. My only other question is whether the law applies to services as well as products. But, if it is a CA law and does apply to services, you are correct: you should be able to cancel the contract within 3 days.
ETA: look on the back of your contract, and/or read all the fine print. There SHOULD be a clause defining your right to back out if indeed that law applies in CA.