If I purchased a car on Friday, but lost my job on Saturday, can I return the car, I have not even had it for 48 hours

Generally, under normal contract law, once you sign a contract for purchase of a car and take it from the dealer's lot, you own it.  However, some dealer's contracts may have clauses allowing you to return the car within a certain time-frame.  But unless the contract you signed contains such a clause, you own the car.  The fact that you lost your job has nothing to do with the formation and binding nature of the purchase contract.