如何使WPF数据模板填充列表框的整个宽度？

<DataTemplate x:Key="MyDataTemplate">
    <Grid>
        <Grid.ColumnDefinitions>
           <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <TextBlock Text="{Binding MyData}"/>
    </Grid>
</DataTemplate>

<ListBox x:Name="MyListBox" ItemTemplate="{StaticResource MyDataTemplate}"/>

public class MyData
{
    public string MyData { get; set; }
}

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();

        List<MyData> dataList = new List<MyData>();
        dataList.Add(new MyData { MyData = "Data 1" });
        dataList.Add(new MyData { MyData = "Data 2" });
        dataList.Add(new MyData { MyData = "Data 3" });

        MyListBox.ItemsSource = dataList;
    }
}