Ok read this; first is regarding this image:
This image will not work as a background-image because it has text, background-images naturally cut-off on the small screens and so does the text that you embedded to it. Please remove this image from being a background add it as an Image element instead.
Make that image 1920px in width so it can cover even the bigger screens.
Another thing with that image is it has a transparent 1px area top and bottom, that is what the white line that we are seeing.
You would not able to see this 1px transparent area unless you open that image on an image editor (e.g. Photoshop), please edit that image and crop those 1px transparent top and bottom area, same goes for the image on the footer/bottom area.
Now to your other question, how to make a section full width and no padding. Please inspect the section and press the Remove Spacing option.
Hope it helps,