Commented Issue: ExpanderView header doesn't fill entire width [10561]

I use the below code for changing the Expanderview header in my own way
<toolkit:ExpanderView.HeaderTemplate>
<DataTemplate>
<Border BorderBrush="Black" BorderThickness="0,0,0,2" Background="#B7ADA1" >
<TextBlock Foreground="DarkBlue" Text="Heading 2"></TextBlock>
</Border>
</DataTemplate>
</toolkit:ExpanderView.HeaderTemplate>
The result i am getting is attached here
How can i make the header center aligned and set entire background of header to screen width as described in the image
Comments: ** Comment from web user: shawnoster **

I adjusted the title to reflect which control the question is about.