Find a nice piece of cardboard. I stole the one (below left) from the back page of a magazene. Using thin strips of masking tape to hold the A3 template, cut the shape out of the cardboard
Now You Can
Place the black carboard under the A4 sheet. Follow the lines with a straight edge and a sharp stanly knife & cut the pattern.
NEXT , using thin strips of masking tape to hold the black template to the plug hole. LIGHTLY FIX. ( all you need is to make sure it does not move when you roll the floorcovering over it.)