Hello, @RoDaAmsterdam14,
That is because you have set your slider images as cover, you have to set them as contain and then the slider image will contain itself in the mobile screen complete: https://postimg.cc/sMLX5n07
OR you can use the Slider Revolution plugin and set the slider with it as per your requirements.
https://www.sliderrevolution.com/documentation/responsive-settings/
Regards 8Themes Team.