The left and right padding of your RelativeLayout is consuming space required by your AdView.

Change RelativeLayout config to :

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
 ...
 android:paddingLeft="0dp"
 android:paddingRight="0dp"
 ...
>

You probably also want to change your AdView config to:

<com.google.ads.AdView
        android:id="@+id/adMobadView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        ...
        />

as you don't really want your AdView to consume the entire screen.