Hi --- It's too late to cancel and get a refund of your deposit in that case even had it been dependent on the balance being financed.
One suggestion is pay the balance on your credit card if possible or a friend / relatives... then re-pay your card immediately using the loan after the work is completed, at least if there are faults or delays, poor / faulty workmanship, bad fitting, bankruptcy or any messing around, you can hold your credit card issuer liable and seek a refund from your CC under the consumer credit act, if you pay cash or cheque you won't have that protection.