If you want to return to the default setting, just change the column and row counts back to what yours was originally. The default on my MacBook Pro Retina display is a 5 x 7 grid, but yours may be different depending on screen size and screen resolution.
You can also choose to just set a custom row or just a custom column count, but you must reset and refresh the Launchpad, and finally killall Dock to relaunch the Dock in Mac OS X and have the changes to take effect regardless of how you customize it.