ViewBox and blurring effect issue? - wpf

Question

I do not understand if it's a bug that I'm causing some with wrong setting or simply a problem of WPF.
I'm trying to see all content of a GroupBox and I'm using the Viewbox as some label without viewBox for a certain resolution are not visible.
Everything works fine, but it seems there is something wrong with the rendering.
As seen from the image:
by setting this in viewBox:
<Viewbox Stretch = "Fill" Grid.Column = "0" Grid.Row = "0" StretchDirection = "Both">
I can see all content but as you can see the labels are blurred and seem to spread so forced, I do not like.
In the other groupbox I tried to set this:
<Viewbox Stretch="Uniform" Grid.Column="1" Grid.Row="0" StretchDirection="Both">
and I get a nicer effect already at the level of rendering:
the problem is that they remain of the white bands on the right and left (if obviously imposed the minimum resolution reached by the software) and this for me is not nice because I do not use all the UI application.
For those wishing to take a quick look at the complete XAML:
<Viewbox Stretch="Uniform" Grid.Column="1" Grid.Row="0" StretchDirection="Both">
<GroupBox x:Name="Ospite_Analisi" Header="Ospite">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="*" />
<RowDefinition Height="*" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Grid Grid.Column="0" Grid.Row="0">
<Label>Inserire scudetto</Label>
</Grid>
<Grid Grid.Column="1" Grid.Row="0">
<StackPanel Orientation="Vertical">
<Label>Nome Squadra</Label>
<Label>Nazione</Label>
<Label>Campionato</Label>
</StackPanel>
</Grid>
<Grid Grid.Column="2" Grid.Row="0" Grid.RowSpan="2">
<Label>Inserire controllo forma</Label>
</Grid>
<StackPanel Grid.Column="0" Grid.Row="1" Grid.ColumnSpan="3" Orientation="Horizontal" HorizontalAlignment="Center">
<Label>Vittorie casa</Label>
<Label>Vittorie fuori</Label>
</StackPanel>
<Grid Grid.Column="0" Grid.Row="2" Grid.ColumnSpan="3">
<DataGrid>
...
</DataGrid>
</Grid>
</Grid>
</GroupBox>
</Viewbox>
What I want to achieve is this:
-Fix Both GroupBox in maximum width (the minimum resolution) in viewBox without losing quality and without making it seem forced rendering. How can I achieve this?