The factory layout is 3 layers: the base QWERTY layer, a Numpad layer, and a Function layer (this is the one with mouse keys and whatnot).
To get back to that layout, the easiest is to use Chrysalis: connect to your keyboard, go to Preferences, then My Keyboard, and there will be a “Reset to factory settings” button at the bottom of the page there. That will restore the original layout.
At the moment, said button will spin indefinitely, but you can restart Chrysalis after about 10 seconds. This is a bug that’ll be corrected in the next Chrysalis update.
You will likely want to upgrade your firmware to 0.90.1, too, probably before doing the factory reset. See this post for more details: