Question GroupBox header not displaying properly

[GreenVicted]

I have a problem i have a groupe box that is not displaying properly, i have to move the entire form (make it swirl real fast ) so it displays properly or simply changing the window
size. It's the bottom of the groupBox that starts at the top.
here is xaml:

<GroupBox Header="Burdens (Kg)" BorderBrush="Beige" Foreground ="Black" Margin="21,101,801,0" Name="GroupBox1" VerticalAlignment="Top" Height="585" Grid.ColumnSpan="2">
            <GroupBox.HeaderTemplate>
                <DataTemplate>
                   <TextBlockText="{Binding}"Foreground="Black"HorizontalAlignment="Left"  FontWeight="Bold" />
                </DataTemplate>
            </GroupBox.HeaderTemplate>
            <StackPanel Name="StackPanel14" Orientation="Horizontal" Height="557">
//Multiple stack panels
</GroupBox>