I had the same problem deciding between the medium or the small flap. I'm also petite, 5"4 size 0 and initially thought to go with the medium since it was obviously the popular choice. But when I tried it on at the store, I felt more at ease with the small (which was weird because I normally prefer bigger bags) but to me, the medium flap looked a tad big for me, yet the small size looked perfect - not too small at all visually. But yes, it really does not hold much which is ok with me because I don't carry much anyway. I think it's really a personal preference. SO, despite the medium being the more popular choice amongst everyone, I ended up getting the small and am loving it!!
Sounds like you're in a panic. I have 2 e/w purses and I love them. They are light as a feather and because they are longer than taller, they fit the same amount as a medium classic. It does not have the double flap, which doesn't bother me but it adds weight to the bag as well as support. The only thing I miss is the little pocket on the back of the bag that I tend to put receipts in, which I empty when I get home. Wait until the bag arrives before deciding you don't want it. I'll eat this messge if you don't like it. You know you can shorted the chain too, which you can't do on the medium/large, mini, or jumbos. There was a post about how that's done with pictures included.
Please post pics of you and your e/w when it arrives!!!