Very nice quilt!
If you change out the white HST's for another row of the pieced squares along the top & 1 side, then add the white HST's back on, that should get you right about in the neighborhood of where you want to be (79x91)".
If you need that 72" vs. 79", I'd go with single 2" finished strip top & bottom (probably in that navy blue that you used), plus a pieced border all around that "finishes" at 6" (the outer edge will be the raw edge that gets enclosed in your binding so you'll actually stop sewing when it measures 6.25"). For the pieced border I'd either go with smaller versions of the squares, on point surrounded by white, or I'd pick a totally different shape (probably circles, but could be triangles or hexagons or even diamonds turned sideways running in a row). Rather than piecing the border shapes, I think I'd go with just a single fabric for each to really bring out all the beautifully patterned fabrics you use in the quilt.