To get the shape you want, use a plastic overlay of your design. Buy the cheap plastic they sell at stores for tablecloths. Take a piece the size of your block and trace your design onto it. Put registration marks on the plastic pattern so that you know where the center is horizontally and vertically. Crease your fabric in the same places and line fabric and plastic up. You will be sure to get your bias vine just placed just right and exactly in the same shape as your pattern call for.