Pin away extra fabric.
Mark your pins, with a pen, and draw lines on the muslin with a ruler. This is the easiest way to see how much fabric to removed from the pattern.
1. Work on the back piece
Transfer all the lines from the sample to the paper pattern. Do it by measuring on the sample and then marking the lines on the pattern. The new lines are red, as illustrated below.
Now cut the red lines. And remove the small pieces.
2. Tape the two pattern pieces together.
Draw a new grainline, perpendicular to the bottom line