Hi Wayne
Your ARF Ringmaster is pretty true to the original....therefore has a "pollywog" rib shape. Typically, film covering is "stuck" to the leading and trailing edges and then shrunk.....this means that it bridges the pollywog porting of the back portion of the airfoil.
It's tough to make other coverings follow the contour of the rib...
Just keep your covering tight and fly it.
Have fun!