WP7 ListBox Items to fill the width of the ListBox

I am trying to get the Items in a ListBox to span the entire width of the ListBox. I have found several posts dealing with HorizontalContentAlignment="Stretch" but I have not been able to get it to work in my WP7 app. Here is my ListBox:

<ListBox Margin="8" HorizontalContentAlignment="Stretch" ItemsSource="{Binding Collection}" >
    <ListBox.ItemTemplate>
        <DataTemplate> 
            <Border BorderBrush="Black" CornerRadius="3" Background="#FFE88D34" 
                BorderThickness="1" HorizontalAlignment="Stretch" > 
                <Grid Background="Transparent" HorizontalAlignment="Stretch" > 
                    <Grid.ColumnDefinitions> 
                        <ColumnDefinition Width="*" /> 
                    </Grid.ColumnDefinitions> 
                    <TextBlock  
                        Grid.Column="0" HorizontalAlignment="Stretch" 
                        Margin="2"                                    
                        FontSize="10" 
                        Text="{Binding Property1}"/> 
                </Grid> 
             </Border> 
        </DataTemplate> 
    </ListBox.ItemTemplate>
    <ListBox.ItemContainerStyle>
        <Style TargetType="ListBoxItem">
            <Setter Property="HorizontalContentAlignment" Value="Stretch" />
        </Style>
    </ListBox.ItemContainerStyle>
</ListBox>

I am trying to get the orange Border to span the entire width of the listbox so that all the list items are the same size and not just the size of the text in the TextBlock.