if the project will be washed you might want to tack the edges- so they do not curl up- sewing right down the center is always an option-but if it gets washed the edges will curl
a permenent glue is always another option- liquid stitch is one but there are many to choose from- the thing about the permentent glues are they are next to impossible to sew through if you do want to add any stitching....and glues (can) gum up your needles....but if you do not intend to sew them at all- it will not make a difference.