Help, Please!. Am I being rip off by the car dealer?

[dozingpanther]

I just purchased a used car today. It was $20699 including tax, registration, plate, and other kind stuff. We've made down payment for $5000, so the amount covered by auto loan is about $15200. When I talked to the finance person, she told me the total interest I will pay is about $9000 for 6 years; the payment is going to $350 per month for 72 months. She then told me buying a warranty plan can lower the interest rate. The original interest is $9000, the cost of the warranty is about $5000, once I purchase the plan, she can make the interest to $4000. Even though these still add up to $9000, at least not all my money goes to the interest, I have a warranty. Because of what she said, I agree to purchase the warranty. So I have to only pay for $4000 interest, but the amount of money we borrowed from bank is $20200 instead of $15200. Not until I got home, I realized something's not right. Based on the deal with the sales man, it should only remain $15200 unpaid. I used online loan calculator, only the annual interest rate is 20% would accumulate interest to $9000 for 6 years. My credit score is in the mid-600, the sales man told me, he said it is not good, but not bad. I think my credit score would bring me a lower annual interest rate than 20%. Am I correct? If the $9000 interest is bullshit, can I cancel the warranty contract? I mean $995 for etching is really a rip off; it only costs $15 outside, not to mention Honda care and other kind of stuff.