If everyone took the day off, and America closed down for one day, it would be 1/260th of a year. One workday out of the entire year. Simple arithmetic. No need for you to complicate it unless you are trying to defend the Socialist Obama.
But much of the value of consumption, production and other aspects of the economy would be made up in other days. All other things constant, much of the economic activity would even out over the year.
As another way to put it, by your logic, adding Sunday to the workweek would increase our GDP by approximately $2.8 billion or so, which is not the case