How to close those green lines?

What video preset are you using? In my opinion, the green lines are a hold-over from the old, analog, standard definition standards where overscan (or cropping of the image) was definitely an issue. It was a common problem with cathode ray picture tube television sets. In modern HDTV standards there is little if any cropping taking place at all. A modern flat screen TV set is typically going to display a full 1920x1080 or 3840x2160 resolution image.

On the other hand, the green guide lines can be useful as a compositional aid. Unless you're running a graphics crawl or ticker across the bottom of the screen or something else that uses the edge of the image it's usually a good idea to leave a decent amount of "white space" or breathing room between graphics elements and the edge of the image. The green guidelines can help keep a motion graphics composition from looking cramped or crowded on screen.