Hi @jennwprez ,
I just checked your site but there is no example with our Transition Slider plugin. But as I wrote once again to our user, the only thing that can be a problem when you put a shortcode from our slider is that the container element you put it in is not fullscreen or maybe it contains some padding that needs to be removed in the theme you are using.
Our slider in fullscreen mode works by taking up 100% of the width and 100% of the height of the element in which it is located, so if you put it in an element that has a small padding along the edge of the page then it will look like a slider is not fullscreen, the only problem is that you need to remove the padding from the element it is in, and that unfortunately has nothing to do with our slider.
Thanks for the inquiry and for using us slider,
have a nice day!