Grid expander header - can't get arrangement right
===

I have the following `Expander` defined for a `DataGrid`. 

    <Expander IsExpanded="True" HorizontalAlignment="Stretch" Background="Blue">
    	<Expander.Header>
            	<Grid HorizontalAlignment="Stretch" Background="BurlyWood"
                          Width="{Binding ActualWidth, RelativeSource={RelativeSource AncestorType=Expander}}">
                          <Grid.ColumnDefinitions>
                          	<ColumnDefinition Width="3*" />
                            <ColumnDefinition Width="*" />
                          </Grid.ColumnDefinitions>
    
                          <TextBlock Text="{Binding Path=Name, StringFormat=\{0:D\}}" FontWeight="Bold" />
                          <StackPanel Orientation="Horizontal" HorizontalAlignment="Stretch" Grid.Column="1">
                          	<TextBlock Text="Total : "/>
                          	<TextBlock Text="{Binding Path=Items, Converter={StaticResource sumConverter}}" FontWeight="Bold"/>
                 	      </StackPanel>
                    </Grid>
        	</Expander.Header>
            <ItemsPresenter />
    </Expander>

I need to display the item name in the left and the sum in the right end of the group header. However what I get is this:

![enter image description here][1]


  [1]: http://i.stack.imgur.com/kyxcE.png

How can I move the 'Total' to the right end of the header?