You say you saved it. Once that's done there is NO way to undo any kind of blur. What you want to do in the future is use an adjustment layer, which is nondestructive, or just copy the background layer and try things out on the new layer. That way if you really mess up, you can just delete that layer and make a new one.
Do note that if you save the LAYERED file you can go back and continue editing, but if you are only working on a single layer or you merge or flatten your layers, you will not be able to undo any editing.
While the file is open, go to Window and select History. The History panel lets you undo much more than Command or Ctrl + Z, which generally only allows one undo. In the History panel you will see each thing you did, and you can click back to the last place you want to undo what you've been doing.
Note that the History in the History panel goes away when you close the file.
