AutoCompleteBox items alignment

[vmiwouter]

Is there a way i can align the items with the box itself when within a grid? Now its too far to left.:

Outside the grid the alignment is correct like blue line, but within another grid its aligns wrong.

Xaml:

<StackPanel Orientation="Vertical" Grid.Row="3" Grid.Column="0" Grid.ColumnSpan="2">
	<Label Margin="3">Prijslijst:</Label>
	<Grid>
		<Grid.ColumnDefinitions>
			<ColumnDefinition Width="100"/>
			<ColumnDefinition Width="*"/>
			<ColumnDefinition Width="Auto"/>
		</Grid.ColumnDefinitions>

		<AutoCompleteBox
				Margin="3"
				HorizontalAlignment="Stretch"
				Watermark="{Binding PrlCode}"
				ValueMemberBinding="{Binding pl_code}"
				SelectedItem="{Binding SelectedArtikel}"
				ItemsSource="{Binding Artikel}">
					
			<AutoCompleteBox.ItemTemplate>
				<DataTemplate>
					<StackPanel Orientation="Horizontal">
						<TextBlock Text="{Binding pl_code}" />
						<TextBlock Text="{Binding pl_desc}" 
									Foreground="{DynamicResource AccentTextFillColorPrimaryBrush}"/>
					</StackPanel>
				</DataTemplate>
			</AutoCompleteBox.ItemTemplate>
		</AutoCompleteBox>
						
		<TextBox Margin="3" Grid.Column="1" Text="{Binding PrlDesc}" IsReadOnly="True"/>
		<Button Margin="3" Grid.Column="2" Content="..." Command="{Binding SelectPrlCommand}"/>
	</Grid>
</StackPanel>