Sew a 5" X 1 3/4" white or off white strip (sashing) to each of 60 5" charm squares.
I used 70 / 72 sq.s so I could use more of the fabrics, but it caused me to have a quarter square in two corners. You'll see below.
Press all the squares open and lay them out in Rows on the floor or table to see where they look best. you should have enough squares to use them on the edges and just cut them off a quarter inch past the points. (I didn't have enough squares to do that, so I cut some of my squares in half into triangles for the edges. It worked just fine even though technically there wasn't an extra quarter inch for the seam.) Sew those squares and their sashings together in these Rows.
Then sew the same width sashing in long strips along the side of each row. Then you can sew the rows together. Try to make sure that your squares stay lined up with each other so they're straight in both directions. Use pins if you need too on long rows like that. You'll notice I have a quarter triangle on this corner (above). I added an extra row to my original plan which forced me to do that. It would be better to do both corners like the one below!
On two corners you'll have the sashing end like this.^ The problem is, it doesn't extend to a square corner. I just took a sashing scrap and sewed it on to the corner. It looks like it's too wide here, but it won't matter.
Then take your ruler and trim like this. ^
OR you could unpick the whole corner (above) and put a new sashing piece in - an inch longer than the first one was.
Put a 2 1/4" border on (same fabric as sashing). Then a 1 3/4" Inner border. And an Outside border however wide you want.
These always look great no matter what line you use!