I'm shocked no one else has had this experience, but the measurements were sadly off for these. I ordered 40.5 inch which should have been the perfect width for my windows based on their guide, but they fail to mention that the mounting hardware sits slightly off the window frame and makes the overall width larger. I tried and I tried and these simply would not fit despite following their measurement guide. 

So incredibly disappointing. I'd think twice before ordering these. If you're willing to pay this price, just get some truly custom window treatments from another company.