Where are our posters getting the idea that they're in a "fully executed contract" - RTL, you're not the only one. Agents say this sometimes, too.
It's only fully executed when everything contracted for happens - deed and money switch hands, et cetera.
You're in an executory contract, the seller still has the deed and doesn't yet have your money.
With that little bit over, the fact is, the ways you can escape are stated in that executory contract, and if there aren't any, and you try to escape, you can be sued for damages, specific performance, and I think in California, be banned from Disneyland for life.