If your Replo page is scrolling to the right instead of up and down on mobile it means some page components exceed the preview dimensions.
Common Causes and Solutions
Often this unwanted behavior is the result of applying desktop widths to your mobile components -- making them larger than the 400px window available on mobile.
To prevent this, one option is to locate the image or component that's causing overflow and setting it to "fill available width" to bring it within page bounds. Apply "fill available width" to all components like images or text to prevent unwanted scrolling.
Adjusting the default preview dimensions from 400 to 200 pixels may help.