If the hole is too big, you can
build it up by gluing a strip of paper inside the hole.
Cut as strip of paper equal to the hole circumference
(3.14 x diameter). Mark off a strip in the middle equal to
the thickness of the cardboard. Fold along the lines. Draw
tick marks at regular intervals.
Cut slits from the outside edge to each of the tick
Turn the strip into a circle and glue it inside the
Fold down the little tabs and glue them to the cardboard
surface on both sides.