Legal Question in Real Estate Law in California

There is a cooling off period for door-to-door sales but not normal commerical sales as buying a car. Otherwlise, people would drive a brand new car off the lot and three days later bring back a used car whose value is much less. People would go to a car dealer instead of a car rental agency.

That it causes you finanical problems is what all big ticket item purchases do. That is not the fault nor responsibility of the seller.

No. You may try to get them to cancel the contract, but you are legally liable on it now.