how stretch user control in tab control item

Hi I try solve how stretch user control width / height which is active in tab control to tab control width / height.

I use caliburn micro.

I create some user control. Here is it:

<UserControl x:Class="Spirit.Views.TabChatView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:Micro="clr-namespace:Caliburn.Micro;assembl开发者_JAVA技巧y=Caliburn.Micro" 
             xmlns:Controls="clr-namespace:Spirit.Controls" mc:Ignorable="d" 
             Name="ChatWindow"
             Background="{StaticResource LightGrayBackground}"
             Height="545" Width="680">[...]</UserControl>

This user control is active in shell, shell declaration is here.

<Window x:Class="Spirit.Views.ChatShellView"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
        xmlns:cal="clr-namespace:Caliburn.Micro;assembly=Caliburn.Micro" 
        Title="ChatShellView" Height="300" Width="300">
    <DockPanel>
        <Button x:Name="OpenTab"
                Content="Open Tab" 
                DockPanel.Dock="Top" />
        <TabControl x:Name="Items">
            <TabControl.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <TextBlock Text="{Binding DisplayName}" />
                        <Button Content="X"
                                cal:Message.Attach="CloseItem($dataContext)" />
                    </StackPanel>
                </DataTemplate>
            </TabControl.ItemTemplate>
        </TabControl>
    </DockPanel>
</Window>

Result if some user constrol is active in this shell you can see on this image:

I would like stretch user control on maximum tab control witdh / height.

Remove Height="545" Width="680" in UserControl definition