It is a little hard to tell from the screenshot (there’s not much context), so you’re welcome to post a zip of your .hype document.
My guess would be that you have multiple Responsive Layouts, but there’s no flexibility enabled that would have elements like your background stretch to resize between the sizes. Please see the flexible layout portion of the documentation:
You would want to enable this, and then turn on the scale pins in the metrics inspector. You can also change the scaling behavior to preserve the aspect ratio, which is often useful for backgrounds. You would probably want to choose Expand to Fill that way it will always exceed the window size.
The What’s new In Hype 2.5 video’s first section also has a basic intro to flexible layout, including doing a background like this.
This just happened to be the asset size, being bigger than the scene has no effect.