Weird. I thought the DoubleNest would be wider.
With those dimensions try starting with a 60" wide piece of fabric and add some 12" pieces to each side. You will probably loose about 3" on each side due to hems and the flat felled seam for attaching the side panels. That is going to put you pretty close to a ENO DoubleNest size in width.
Great.Now I wanna make a wider hammock.