Make Columns to have alignment = right

Goal:
Make the column "Drop in" and "Total platser" to have text alignment = right.

Problem:
I tried doing it my using XAML code but it didn't work.

Information
- I'am using Nhibernate to retrive the data.
- This is a usercontrol.

<ListView x:Name="lvw_aktivitet" HorizontalAlignment="Left" ItemsSource="{Binding}" SelectionMode="Single" Height="337" Margin="217,147,0,0" VerticalAlignment="Top" Width="356"><ListView.View><GridView><GridViewColumn Header="Tid" Width="auto" DisplayMemberBinding="{Binding Path=Tid}" TextBlock.TextAlignment="Left"  /><GridViewColumn Header="Aktivitet" Width="auto" DisplayMemberBinding="{Binding Path=Aktivitet}" TextBlock.TextAlignment="Left"  /><GridViewColumn Header="Total platser" Width="auto" DisplayMemberBinding="{Binding Path=Total_platser}" TextBlock.TextAlignment="Center"  /><GridViewColumn Header="Bokade" Width="auto" DisplayMemberBinding="{Binding Path=Bokade}" TextBlock.TextAlignment="Center"  /><GridViewColumn Header="Drop in" Width="auto"  ><GridViewColumn.CellTemplate><DataTemplate><TextBlock TextAlignment="Right" Block.TextAlignment="Right" Text="{Binding Path=Drop_in}"/></DataTemplate></GridViewColumn.CellTemplate></GridViewColumn></GridView></ListView.View></ListView>

        private void DisplayActivityForToday()
        {
             DateTime aa = (DateTime) cdate_left.SelectedDate;

             lvw_aktivitet.DataContext = _myNhibernateDataProvider.RetrieveAllActivitetBasedOnDate(aa);


        }