A few thoughts:

1. When adding classes via JavaScript, we try to name them based on state (.is-hidden, .is-shown, .is-fullscreen, etc.). fit-to-screen seems not to represent state.
2. This class mentioned above should also control all styling and display properties for the element it is being toggled on and off. With that said, you don't need to call JQuery's show() method and can move the display:block/none rules into your SCSS/CSS