Life should have an Undo button. The best feature PhotoShop has is the Undo button.
Just go to the “Edit” menu and you’ll see Undo. If you’ve done something you didn’t want to, or have reconsidered, just click Undo and you’ll be back one step. Or you can use “Step Backward.”
If you’ve made a few changes that you want to undo, use the History palette and just move up to where you wish you were before you screwed up. For more information on the History palette, go to the post “History Palette.”