One method that works well if you are not accomplished at applique is to face the circle. I suggest using a light weight fusible interfacing such as Pelon F911. Draw the finished circle size on the back of the interfacing. Place fusible side against right side of fabric and sew around the line. Cut out leaving a scant 1/4" seam allowance. Seperate with fingers and cut a slit in the interfacing center. Turn the whole thing inside out and smooth the edges. Then lay the circle on your block and press in place. Put a piece of paper under the block to protect the ironing board. This will hold long enough for you to machine or hand applique in place. Once your applique is complete you can turn the block over and trim the excess away.