The finished size of the sides of the center square should be approximately 5-5/8 instead of 5-7/8.
Theoretically, the finished side length should be "the square root of 32" - which is approximately 5.657 - which is fairly close to 5-5/8 - which is 5.625.
I actually prefer to cut my triangles around a template instead of cutting squares diagonally. When I cut around a template, the triangles are actually a smidge larger than when I cut a square diagonally. I consider myself a fairly accurate sewer, but when I do the cut the square diagonally with only 7/8 extra method of making HST's - they are ALWAYS skimpy!- even when I move the needle over a couple of clicks to make a narrower seam.
So - if one chooses to do the cut the square diagonally method - ALWAYS add one whole inch to the finished size. I think part of the loss is in the actual cut (think of a saw going through wood) - and part is lost in the turns of the fabric when the unit is opened up.Some also say that the bulk of the thread also uses up some of the dimensions.