I've had a few requests for more complete directions so I decided to polish up my notes and put a free download up on Ravelry. They make such nice, useful gifts and are so much fun! I'm adding a little photo tutorial here on the trimming process.
This is what your unfelted 'square' will look like -
and here it is after felting. Looks a little rough around the edges :)
This is easiest with a rotary cutter. I'm sure it could be done with very sharp scissors, but I think you'd want to mark your cutting lines first somehow - maybe with masking tape.
I started with one of the wavy edges and laid my ruler so that I would cut the minimum while still getting a clean edge. It helps if you have your work squared up with the grid on your mat and refer to the lines when placing your ruler.
Then I turned it 90° and cleaned up the next edge, making sure that the second cut was perpendicular to the first.
Turn again, align the ruler, cut.
After the last cut, you will have this -
Mine wasn't quite a perfect square, but the quarter inch difference I had is not noticeable once you cut it into 4 pieces.
Make the first cut so that it goes down the middle of your square:
Stack them up and tie a pretty bow around them -
The perfect hostess gift!