Can I return a used car that was sold with extensive corrosion rendering unfit to drive?

I bought a used car almost two months ago from a Honda dealership after they inspected the car and sent it to a subcontracted mechanic who specializes in BMW for a pre-purchase inspection. They sold me a warrantee for two years, telling me that it would "cover everything but a moonroof" (which I dont have) for almost $4k. The car immediately started having lights come on and now it is back at the shop with a repair bill that will probably run more than the car is worth due to corroded cables that they didn't discover until now AND they say that it isn't covered under my warrantee. The car is unfit to drive now even if i wanted to. WHAT CAN I DO?