Block 5, the Square in a Square in a Square, needs a size correction:
Step 2, Unit B, will be 4.75" unfinished, not 4.5". Cut C squares 3" or larger for those half-square triangles.
I didn't catch this because I paper pieced these blocks so just cut everything bigger.
IF YOU ALREADY TRIMMED Unit B to 4.5", simply cut the D squares 4-4.5", add them and trim the finished block to 6.5". Your center square will "float" just a bit, no problem.