I don't have a total contract amount, is my contract unenforceable because of lack of terms?

If I understand you correctly, the contract states a deposit amount and then a monthly amount, which you are to be paid for the succeeding 12 months, and your question is whether the contract is too indefinite to be enforced because the arithmetic to set forth the total amount was not included in the written agreement.  While I am not familiar with California law specifically, if this is the only issue with the contract, I don't see it as an issue.  There are many contracts like this.  When you rent a car, for example, the contract provides that you will pay a certain amount per day.  The same when you stay at a hotel.  When you hire a catering  hall for an affair, you agree to pay a certain amount per guest (with a guaranteed minimum.)  Employment agreements may provide for a certain amount of compensation per hour, or even by work done (i.e. $20 for every bushel of lemons picked.)  The terms are clear.  If you agree to pay $100 per plate and you have 100 guests, you owe $10,000; if you have 120 guests, you owe $12,000.  If you agree to work for someone for $10 an hour, and you work 10 hours, you are owed $100.  There is no need to do the multiplication in the contract itself.