I think the ruler is the problem. You need to use a triangle ruler WITH a point, not one of the ones where the point is cut off. I think this may be the problem. the book is very specific on this. You could try to turn your ruler so one of the points is pointing up, and put a piece of colored tape where the 3 3/4" line should be. it looks like the yellow numbers on the ruler may be the finished triangle size.