Your viewport is not optimised and a customer needs to horizontally scroll to view your content on their device. Your content should only ever have a vertical scroll and not a horizontal scroll.
To create a great experience for a customer they should only need to scroll vertically so it is important to remove the need for a horizontal scroll.
The viewport can vary significantly over different devices so it is important to use a relative size rather than a fixed pixel size. Your should configure your viewport a relative size such as width:100% rather than a fixed size. A web developer can make this adjustment to your viewport to ensure your pages render correctly on each type of device.