Using a loop turner, turn your piece out the correct way. Iron piece flat with seam on the edge, be careful not to iron over your already ironed up edges.
Thread elastic up through fabric tube and pin down at one end. Use the loop turner to go up inside the tube and hook the other end of the elastic, pull through and pin both ends of elastic together.
Overlap ends of the elastic by 0.50 and use a zig zag stitch to secure elastic ends or make a knot.
. Push raw edges of fabric tube inside and overlap one edge of the tube as shown. Sew down, securing both ends of tube and elastic inside.
Now go and make your is easy.