The instructions say to trim the 1/2 square tris (5" squares...trim the 1/2 square tris to 4-1/2")...This is so your 1/2 square tris are accurate....many patterns show to do this now.
They don't repeat the trim to size in the smaller block instructions...should have, but, thinking they assume that since you trimmed the larger, you would know to trim the smaller.... not sure that I would have, until the 1/2 sq tris didn't fit.