I'm having the same problem with a similar Valentino bag (Small Rockstud Leather Crossbody Bag).
It is a crossbody bag that seems to indent/sag in the middle because the strap pushes against it. Neiman told me I could bring it in and they'd redo the straps so that they are on the outsides of the bag, but I am hesitant to go that route. I am trying to stuff it with socks while I am not using it in hopes that the bag will get used to being puffed out more. Pretty disappointing (my first full-priced Valentino bag; the other one I found at Off Fifth for a great price and it is holding up better).