Cut the corks in half length-wise with a sharp knife. A pocket knife could work, but a sharp kitchen knife would be more efficient if you can deal with the potential of the knife dulling because of this project. If you have rough or uneven edges on the cork after cutting it, use sandpaper to smooth them.
Arrange the corks into a rectangle or square to give yourself a general idea of the shape and size of your bathmat. Use the yardstick to make sure each side is straight and then take a rough measurement.
Cut a piece of the shelf liner with the scissors so it is the size of your rough measurement.
Line the outside of the shelf liner with the corks so it looks like a frame. Apply a generous amount of glue to each cork, keeping it about 1/8 inch from the edge, and press down firmly. Remove any excess glue that seeps from under the cork before it dries.
Fill in the middle of the liner with the corks. Do not glue the corks down immediately as you transfer them into place. Make sure they all fit and rearrange the corks as necessary and then glue them down one at a time to finish your bathmat.