I think the issue was with the 45 degree line of the ruler being laid on the seam line and not the edge of the fabric, if you do not want the points cut off. If your sewn fabric strips are the same width as the solid strip, and you cut, sew and press accurately, the pattern is easy to do.
If your ruler is taller than your fabric strips, line the fabric strips along a line on your mat and then align the 45 degree line of your ruler along another line below it, so you keep your ruler straight when cutting.