Except in lieu of the center pleat, I cut the bottom pattern piece just about in the middle, and spread it apart about 2-3 inches to add side gathers. Like so:
The fabric is a delicious ivory linen (I think it's a blend though - doesn't winkle as hardcore as 100% linen - hooray). I bought this fabric at Joann's last summer! They often have stuff just like this though... Linens or 'linen-look's. It's such a dream to sew with.