Jeanie, the triangles are both the wrong size. Here is how I figured it out.
I used the corner block to come up with the correct size small triangle and when I sewed the side blocks together that strip was too short to sew to the large square made from the triangles so I squared the large triangles I sewed together by the length of that strip. I added the final triangle after everything else was together and squared it up and it came to a perfect 8 1/2.
Hope this helps. Honchey also posted an alert a couple weeks ago that the angle side of the triangle should be 4 1/2 inches but the template is 4 7/8