You would cut the rectangle a bigger 'height'. For instance a common size would be to cut the rectangle 2.5X4.5 inches, and the squares 2.5 inches. If you cut the rectangle 3X4.5, and keep the squares at 2.5 inches, you will get a goose unit that finishes at 2.5X4 and has a white margin. To keep the finished unit at 2 x 4, paper pieceing would be a good option.