It's time for geometry homework, but you can't find a model of a cube to use for reference. With just a dollar or two worth of materials and a few minutes' time, you can make your own cube to suit your needs.
Cut two of the straws in half. There is no need to measure the pieces, simply fold the straw in half and cut at the crease.
Form the four uncut straws into two squares by bending them in half.
Place small amounts of super glue on the edges of the bent straws where they meet. Affix the glued ends to one another so that you have two squares. The straws should not overlap as you are gluing the squares.
Place glue on both ends of each of the four cut straw pieces. Attach the two squares to one another by gluing the four cut straw pieces between the four corners of both squares.