A mortgage is a lien against the house/property, with the house and property as collateral. How could it be collateral, if you don't already own it?
Check out the terms of the mortgage and note you signed. Is there a prepayment penalty clause? If there isn't, then when you make your monthly payments, include how much ever extra money you can afford every month to reduce the principal balance. (It doesn't have to be the same amount every month.) Make sure you include a note specifically stating that "the excess funds are to be applied against principal only"... and use those exact words.
If you aren't sure about prepayment clauses, call your lender (or whoever the lender sold the mortgage and note to), ask for the mortgage loan servicing dept., and ask them about it. They have that info.