Remedies for bad auto loan

Recently financed a car through a small used auto lot. Was told I was financing $3000 and paid $1000 down on car advertised for $4900. Was told I was "cut a deal" since I could not put $1900 down. Found out the financed principle is $6100 not $3000. The car has several things wrong with it, all non mechanical, but car was advertised as great condition. Its a convertible and the top not only does not go down, but leaks. I was never given a copy of the contract. The only thing I signed, I was told was a application with preliminary numbers. Apparently that was my contract? Finance company says lot should give me contract, lot said finance company. Car needed gas (barely made it to a station), oil change, and 3 tires immediately leaving the lot. First tire went down in a parking lot 2 days after taking possession.