Legal Question in Real Estate Law in California

What can and can not be done depends almost entirely on the written contract of sale of the property. If the contract does not forbid early payments then you can make them [excess amount goes to principle]; if the contract says nothing about a credit for rents paid, there is no credit [at the time you paid rent you were a tenant and not an owner so none of your payments normally would go to the ownership of the property].

You should have your contract reviewed by an attorney. I cannot tell from your limited post whether you have a lease with an option to purchase, a lease that became a purchase and sale contract, a purchase with an owner carry back, or an installment land sale contract. All of these involve special issues of law.