Undo and Redo
If you make a mistake, do not fear, for Excel has an Undo button that will undo your last action. In fact it can undo a lot more than that.
Simply click the Undo button on the Standard toolbar or press Ctrl + Z and your last action is turned to dust. The drop down arrow to the right of the undo button will list your previous actions, which you can then click to undo.
Naturally there is also a Redo button on the Standard toolbar , or keyboard shortcut Ctrl + Y that will redo the action previously undone. This also has a drop down arrow to display a list of the actions you can redo.