Android Dialog: Cannot Enlarge

I have implemented a dialog but I cannot get the dialog to occupy a larger width of the screen. Is this a problem with my XML?

XML:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://ift.tt/nIICcg"
    android:layout_width="fill_parent"
    android:orientation="vertical"    
    android:background="@color/butGreyBack"
    android:weightSum="60"
    android:layout_weight="60"
    android:layout_gravity="center"    
    android:layout_margin="0dp"
    android:layout_height="fill_parent">

    <LinearLayout 
      android:layout_width="fill_parent"
      android:orientation="vertical"
      android:layout_height="wrap_content"
      android:layout_gravity="top"
      android:weightSum="60"
      android:layout_margin="0dp">

      <TextView
        android:id="@+id/tv_title"
        android:layout_width="wrap_content"
        android:layout_height="0dp"
        android:layout_gravity="center"
        android:layout_weight="30"
        android:text="Default Title"
        android:background="#00000000"
        android:textColor="@android:color/white"
        android:textSize="22sp"        
        android:layout_margin="0dp"     
        android:gravity="center" />

      <TextView
        android:id="@+id/tv_prompt"
        android:layout_width="wrap_content"
        android:layout_height="0dp"
        android:layout_gravity="center"
        android:layout_weight="30"
        android:text="Are you sure?"
        android:background="#00000000"
        android:textColor="@android:color/white"
        android:textSize="18sp"        
        android:layout_margin="0dp"     
        android:gravity="center" />

    </LinearLayout>      

    <LinearLayout 
      android:layout_width="fill_parent"
      android:orientation="horizontal"
      android:background="@color/butGreyBack"
      android:layout_height="wrap_content"
      android:layout_gravity="top"
      android:weightSum="60"
      android:layout_margin="0dp">

      <Button
        android:id="@+id/butOK"
        style="@style/GreyButtonTheme"
        android:background="@drawable/custom_button"
        android:layout_weight="30"
        android:layout_gravity="left"
        android:text="OK"/>

      <Button
        android:id="@+id/butCancel"
        style="@style/GreyButtonTheme"
        android:background="@drawable/custom_button"
        android:layout_weight="30"
        android:layout_gravity="right"
        android:text="Cancel" />

    </LinearLayout>

</LinearLayout>