Lay a plastic tarp down over the floor, if you have not already done so. Put on safety glasses and a hat to protect yourself from the texture as it falls off.
Feel the texture over-spray with your hand to see if it's still damp to the touch. If not, fill a spray bottle with water and spray a light layer of water over all of the over-spray areas to soften them. Let the water sit for one to two minutes.
Place the blade of a drywall knife, or a wide putty knife flat against the ceiling. Pull the blade over the areas of ceiling where you don't want the texture to scrape it off cleanly.
Repeat the process to scrape the over-spray off any of the walls that you don't want it on.
Roll up the plastic tarp to collect all of the texture residue and place it into a trash can.