CA Civ Code Section 1689.20

(a)

In addition to any other right to revoke an offer, the buyer has the right to cancel a seminar sales solicitation contract or offer until midnight of the third “business day” after the day on which the buyer signs an agreement or offer to purchase which complies with Section 1689.21.

(b)

Cancellation occurs when the buyer gives written notice of cancellation to the seller at the address specified in the agreement or offer.

(c)

Notice of cancellation, if given by mail, is effective when deposited in the mail properly addressed with postage prepaid.

(d)

Notice of cancellation given by the buyer need not take the particular form as provided with the contract or offer to purchase and, however expressed, is effective if it indicates the intention of the buyer not to be bound by the seminar sales solicitation contract or offer.