Screen shot attached. As you can see the grid does not fit the full width of the tile and you have an extra column on the right hand side.
<Grid x:Name="LayoutRoot" HorizontalAlignment="Stretch">
<Grid.RowDefinitions>
<RowDefinition Height="*" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<telerik:RadGridView x:Name="radGridView1" AutoGenerateColumns="True" Margin="5" Grid.Row="1" HorizontalAlignment="Stretch"
/>
<TextBlock Grid.Row="0" VerticalAlignment="Top" HorizontalAlignment="Center"
Foreground="Black" FontFamily="Arial" Margin="5" x:Name="tbTitle" >
</TextBlock>
</Grid>