XML : Ad is messing up layout?

I want a layout similar to this:

Here is my XML:

  <?xml version="1.0" encoding="utf-8"?>  <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"      android:layout_width="match_parent"      android:layout_height="match_parent"      android:orientation="vertical"      android:padding="16dp"      android:weightSum="100"        xmlns:ads="http://schemas.android.com/apk/res-auto"      android:background="@drawable/blurbackground">        <LinearLayout          android:layout_width="match_parent"          android:layout_height="100dp"          android:orientation = "vertical"          android:weightSum="1">              <TextView              android:layout_width="match_parent"              android:layout_height="wrap_content"              android:text="High Score"              android:textColor="#FFFFFF"              android:textSize="35sp"                android:id="@+id/highscore" />            <TextView              android:layout_width="match_parent"              android:layout_height="wrap_content"              android:layout_marginTop="20dp"              android:text="Score"              android:textColor="#FFFFFF"              android:textSize="35sp"              android:id="@+id/score" />          </LinearLayout>        <LinearLayout          android:layout_width="match_parent"          android:layout_height="match_parent"          android:orientation="vertical"          android:weightSum="3"          >            <Button                android:layout_width="300"              android:layout_height="90dp"              android:text="Share high score"              android:textSize="20sp"              android:textColor="#FFFFFF"              android:background="@drawable/buttonshape"              android:layout_gravity="center"                android:layout_weight="1"              android:onClick = "shareButton"              />            <LinearLayout              android:layout_marginTop="30dp"              android:layout_width="match_parent"              android:layout_height="match_parent"              android:layout_weight="1"              android:orientation="horizontal"              >                <Button                  android:layout_width="0dp"                  android:layout_height="50dp"                  android:layout_weight="0.5"                  android:text="Try Again"                  android:textColor="#ffffff"                  android:lines="1"                  android:textSize="13sp"                  android:onClick="tryAgain"                  android:background="@drawable/buttonshape"                  />                  <Button                  android:layout_width="0dp"                  android:layout_height="50dp"                  android:layout_weight="0.5"                  android:text="Level Select"                  android:textColor="#FFFFFF"                  android:textSize="13sp"                  android:onClick="levelSelect"                  android:background="@drawable/buttonshape"/>               <LinearLayout />     //THIS LAYOUT MESSED EVErYTHING UP!!!                 android:layout_width="match_parent"                 android:layout_height="match_parent"                 android:orientation = "vertical"                 android:layout_weight="1"                 >                   <com.google.android.gms.ads.AdView                     android:id="@+id/adView"                     android:layout_width="match_parent"                     android:layout_height="wrap_content"                     ads:adUnitId="@string/banner_ad_unit_id"                     android:layout_alignParentBottom="true"                     ads:adSize="BANNER"/>                 </LinearLayout>            </LinearLayout>          </LinearLayout>      </LinearLayout>    

And it was going all fine until I added an adview at the bottom, which messed everything up. How can I fix my layout, and why is my adview not at the bottom?