Seems like we are all having different experiences. When I sewed the light triangles to the dark I trimmed to 8.75 and came out with all points plus the .25 inch. I cut the squares for the outside triangles to 7.75. Then trimmed to 12.5. Worked out for me.
Love the way this is coming out. Would love to try some of the crumb pieces in that last triangle but for now just going with the one fabric.