how do I recalculate my down payment available

I want to borrow 12,000 at 2.99 interest with no money down.

Make the down payment $1 so the calculator can proceed to the next step. I did a quick calculation for you. Borrow $12,000 at 3% for six years and no money down. You will have 72 monthly payments of $181.66 each. Total interest paid is $1080 for this loan.

What you want and what you can actually borrow are probably two different things.