i cut each panel to 13.5″ x 41″. see the math there? add .5″ to the width for your seam allowance, and for each panel, add 1″ for seam allowance. since mine was 80″ long, each panel needed to be 80″÷2+1″, which is 41″.
2. cut your fabric. cut out your panels and iron them.
3. pin your panels. take the two pieces of fabric that are going to be the top, and pin the 13.5″ sides right sides together on one side. sew that side together, so now you have one long piece, instead of two shorter panels. do the same with the fabric you’re using for your backing. iron everything 