I didn't have enough to cut it lengthwise and didn't want to buy new fabric just for this project. Even if I did I'm not sure I'd want to spend $20+ for each one (it's about 76" wide). Good idea about using a 2nd tension rod. I have one on hand so I can give that a try.
eta: the seam that shows is actually between the green strip and the fabric next to it. The seam up the center doesn't really show since it's gathered.