If you were asked to "explain" the design pattern then there was no need to write any code - you'd have been better off putting in words what the design pattern tries to achieve and possible adding a UML diagram.
Failing that you could have put some comments in your code to demonstrate your knowledge of the pattern.
Your Main function should actually show a change of state and then roll-back to the previous state to fully demonstrate the pattern.
Have a look at this example for comparison
http://www.dofactory.com/Patterns/PatternMemento.aspx[
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