Other mistake: They go to Texarkana, Texas, to pick up the beer, and later in the movie, they are in Fayetteville, Arkansas. Why would they go due north to Fayetteville to get to Atlanta, which is East?
Other mistake: Susan gets upstairs as Iris shows her the room. She manages to miss the naked woman lounging in bed - watching the scene, it's an impossibility. It might not be the proverbial elephant, but it's just something so very unusual and conspicuous in the room, in a spot perfectly in line of sight that it makes no sense Susan would miss it and be surprised by that later. (00:08:20)