Fabrics of any shape can be used, as long as the piece covers the required area. I usually cut strips with a straight of the grain edge that will correspond with one of the sides of the area to be covered.
Using your first fabric, place the fabric right side up on the unprinted side of the paper triangle. Check with a light source to insure the space is covered. Then baste in place with a long machine stitch.
Take the paper, fabric attached, to the cutting board. With the printed side toward you, lay a ruler along the edge of piece one. Fold the paper back - a good knife-edge crease. Lay your ruler on top of the paper, allowing 1/4" extra for the seam you will be sewing. Trim. Do this with the other two sides.
fabric basted to pattern
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printed side, basted
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knife-edge fold, add 1/4"seam
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