How to make ContentControl stretch horizontally

I've set the HorizontalAlignment property to stretch but it did not help. I need that content control since in my real code the DataGrid is injected with prism into the content control. XAML: ``` <ContentControl HorizontalAlignment="Stretch"> <Grid> <Controls:DataGrid ItemsSource="{Binding Persons}"></Controls:DataGrid> </Grid> </ContentControl> ``` Code behind: ``` public partial class MainPage : UserControl { public List<Person> Persons { get; set; } public MainPage() { Persons = new List<Person>(); Persons.Add(new Person { Name = "A",Age = 5}); Persons.Add(new Person { Name = "A", Age = 5 }); Persons.Add(new Person { Name = "A", Age = 5 }); InitializeComponent(); DataContext = this; } } public class Person { public string Name { get; set; } public int Age { get; set; } } ```