Screen cannot be shown completely

The menu is shown only as a tab above, and it is not completely shown at 100%. Can it be shown fully without being cut like that?

Even though I already separate those menus at Navigation and Menu, why it is displayed in one row like that?

The Menu is only used in mobile display.
If you need so many visible tabs, you might be better off having them on the side.
You can change that in Settings → Appearance.