Looking at the images provided, it appears that when the camera is set to current, either the background does not move so it is centered in the camera's view or the background does not scale to fit the size of the camera. Since some of the sky and mountains are cut off in the first image, I'm thinking it is likely a scaling issue.
What node is your background image using? If it is a Control node, you probably need to set it to have an anchor/layout mode of Full Rect
, so it scales to cover the background of the camera. If it is a Node2D node, then you may need to adjust your project settings and their expansion modes and/or write a script that keeps the background image centered in the camera.