If you are working with a cotton fabric, or a similar blend fabric, here is a trick that might save you time and frustration. And, if you don't want to line the piece but just hem it.
TIP ONE - Using a dull knife (like a butter knife) you can score the line you want to fold back on. This is especially helpful when working with curves. Place the fabric on a piece of cardboard (not corrugated cardboard) like a shirt cardboard. Then press down the dull blade and carefully score the line of the fold.
TIP TWO - Here is another way to score fabric that is good for slightly heavier fabrics, Trace the pattern onto the fabric and using your sewing machine with the thread removed just sew along the fold line. The needle will create a punch line that will make folding the fabric back easy and accurate.