Can I give an owner financed property back?

I bought a commercial property through owner financing. Now the city is imposing all kinds of things like a brand new parking lot, retention pond, all kinds of things that cost about $15,000. I do not have the money right now to do it. They will not let me make repairs to the building until it has all these things. Now the city is saying they are going to condemn it and tear it down, unless we fix it up. But they won't let us make repairs until we do the parking lot, etc... We are caught in a trap. The people who sold it to us knew this would happen. What will happen to us if we just quit making payments and give the property back? It was owner financed to us, can they do anything to us if we just give it back?