Try Linda Franz's Inklingo site where she sells all kinds of downloadable, printable shapes. So accurate. Actually, I'd turn those edges by making a durable template of a clamshell shape in desired size. Then, using an oh-so-light interfacing (or fusible, but watch out for stiffness) trace a number of individual shapes onto the interfacing. Be sure to leave some space between your tracings as they'll be easier to cut out in squares.
Then, lay the interfacing square with the single traced shape on top of the right side of the fabric. Sew around the curved top with a somewhat small stitch. Now (good TV project), trim to a manageable seam allowance, clip curves, and gently turn, easing out the seam so no puckers (Those little plastic turners work well here). Iron well (unless using fusible ... sew fusible side to right side so when turned, fusible is ready for the base fabric).
Now, all the top edges are turned. Pin the top row on. Attach to the foundation fabric. Pin the next row in place so that the top rounded edges of Row 2 are just covering the curves at the bottom of Row 1. Attach to the foundation fabric, and so forth until completely assembled in desired size. NO HAND SEWING!
Incidentally, some of the lightest-weight material I've found for this type of applique' are used dryer sheets. They facilitate turning and add practically no weight or bulk of their own.
Let us know how you do. Progress reports, please!