Aspect ratio difference. The viewport in editor is more square. The in engine preview is just that, a simple preview. It's relatively WYSIWYG but not exactly 100%. Also looks like you are using some editor plugin to have the editor and the debug runtime run inside the same window, which might affect it perhaps too.
The offset itself is likely as @xyz said, some offset applied to camera, either manually via inspector or by script. If not the loader thingy. Could also be you are using some TPP template that tries to apply an offset for 'over the shoulder' type character controller.
First I'd look at your script and check the inspector. If nothing obvious strikes out from there next I'd try to remove the external influences such as that loader/launcher thingy.