By law he is supposed to give you that form for cancellation. You should communicate to him by email or mail within 3 days.

Homeowners who enter into contracts with contractors to improve, remodel or repair their homes almost always have a right to cancel the contract, without any penalty or obligation, within three business days after signing the contract. A homeowner may also have a right to cancel a contract after three days  in limited, extraordinary situations.

B. Consumer's Right to Cancel

A buyer can cancel a home solicitation contract without giving a reason or showing any legal cause, and, without penalty or obligation, by giving the seller written notice of cancellation within three business days after the buyer signs the contract.¹³

To cancel, the buyer need only give the seller a written statement (for example, a letter or e-mail message) stating the buyer's intent not to be bound by the contract.¹⁴ If the seller has not complied with certain notice requirements, the cancellation period begins when the seller has complied.¹⁵ If the buyer's signature was produced by fraud, the cancellation period may extend indefinitely. ¹⁶

Check this out: http://www.dca.ca.gov/publications/legal_guides/k-10.shtml

Disclaimer:  The materials provided below are informational and should not be relied upon as legal advice.

You need to read the contract carefully and see if it specifies any special form or any format for cancellation.  As you ready the contract, pay special attention for any penalties of sortx you may face for cancellation, such as forfeiting your deposit.  Once you are certain you want to cancel the contract, give notice of cancellation.  If there is a special form or format required, follow that.  Otherwise, prepare your own notice of cancellation.  Your best bet is to give cancellation notice in a manner that it can be verified.  I would send it by Fax and by Certified Mail, especially if the Fax machine prints out a confirmation sheet. 

Best of luck to you, and be sure to consult your own attorney to protect your legal rights.