Okay, so the ball bag wasn't quite finished. Yesterday I took it over the school to give to the Middle-school coach. Naturally she wanted to try it on the stand to see how it would work. This was my first time to see what the stand actually looked like, and it was very different from I was expecting.
I was thinking it would sit flat on the floor and have it's 4 slats coming out at an angle the length of the original bag. As you can see it's quite different from that idea! Because of it's X shaped design and long length of the top slats the bag slid all the way in causing the sides to fall downward. If I had had the stand with me during the bag's construction I would have been able to make the appropriate adjustments, namely shortening the middle section and side pieces so that they would be taunt.
So I brought the bag back home and made a few alterations. First off, I had to figure out how much extra fabric there was.
Then I sewed 4 darts down the sides. And voila! It now fits taunt! Unfortunately, it still doesn't fit as nicely on the stand as I would wish, but everyone was extremely happy with it when I took it back to the school today. :-D