Check that you don't have a system setting that enlarges the screen, effectively making the screen smaller. Lupa fits around most devices in most configurations but there are some cases where we stub our metaphorical toe.
If you are using an iPhone 6 / 6s / 7, see this article on Apple's support site for how to set / unset "Display Zoom". Other device manufacturers have similar features. If you need help, chat with us (look down and to the right) and we'll try figure it out with you.