If you have done other sashings and cornerstones, then this will be no problem. Add the sashing on one side of each block then put them in rows on your design wall diagonally. One, then three, then five, etc. When you get to the center decrease by two. Add the setting triangles on the end of each row as you sew the rows together. Corner triangles last.
Here's a chart to show you how many blocks, sashings, etc.
http://quiltville.blogspot.com/2010/...ing-chart.html It looks like with 68, you can go 6X6 or make 4 more and do 6X7.
Here's the one for cutting the setting triangles and corner triangles.
http://quiltville.blogspot.com/2005/...nt-quilts.html
Find a picture of a on point quilt and keep it handy for reference. I know my fist one was confusing to me.