This sofa and loveseat presented a challenge. My client ordered all that was available, but there was not enough of the green fabric to make everything. It helped doing a contrasting welting, but, still, there wasn't enough. The solution we (my client and I) came up with was to use the same fabric in white on the back sides of the cushions.
My client can kind of mix and match. In this picture, the back cushions are turned to the white side.
In this shot, the white sides are showing in both the seat and back cushions.
Sofa back, which doesn't show as it is against the wall. My client's 18 year old son was very sweet when he said, "But all your good work doesn't show back there." Yes, but the loveseat's back side does show, so all is not wasted!
The loveseat with all green showing. (To the left you can see a pink chaise. That is the next project.)
And from the back, the white shows a little, but it doesn't look bad.
Sometimes there simply isn't enough fabric to do what you really want to do. If you can be open to creative solutions, you just might get something even better than your original idea. In this case, my client has kids and 3 active dogs, including a 10 month old St. Bernard puppy, so she chose a polyester fabric that can be washed and will stand up to the abuse it is sure to receive.