DataGrid - Last column lengthens too long

I have a datagrid displaying data from a table in a MySQL database. If all columns are with Width="Auto", when resizing the window the grid does not match. If I put it in the last column Width="*", it works as I wanted, following the resizing of the window, but opens with the last column overdue!

How can I get around this?

The code is as follows:

<Window x:Class="DataGridBind.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:DataGridBind"
    mc:Ignorable="d"
    Title="DataGridBind" SizeToContent="WidthAndHeight" >
<Grid Background="GhostWhite" >
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto" />
        <RowDefinition Height="Auto" />
    </Grid.RowDefinitions>
    <GroupBox Header="Tabela: Produto" Grid.Row="0">
        <StackPanel Orientation="Vertical">
            <DataGrid AutoGenerateColumns="False" Height="Auto" Width="Auto" HorizontalAlignment="Left" Name="dataGridProdutos" ItemsSource="{Binding Path=carregarDados}" CanUserResizeRows="True" AlternatingRowBackground="GhostWhite"  AlternationCount="2" CanUserAddRows="False">
                <DataGrid.Columns>
                    <DataGridTextColumn Binding="{Binding Path=idProduto}" Header="Código" Width="Auto" IsReadOnly="True" />
                    <DataGridTextColumn Binding="{Binding Path=ProdutoNome}" Header="Nome" Width="Auto" IsReadOnly="True" />
                    <DataGridTextColumn Binding="{Binding Path=ProdutoPU}" Header="Preço Unit." Width="Auto" IsReadOnly="True" />
                    <DataGridTextColumn Binding="{Binding Path=ProdutoStock}" Header="Stock" Width="Auto" IsReadOnly="True" />
                    <DataGridTextColumn Binding="{Binding Path=ProdutoStockMin}" Header="Stock Min." Width="Auto" IsReadOnly="True" />
                    <DataGridTextColumn Binding="{Binding Path=ProdutoStockMax}" Header="Stock Max." Width="Auto" IsReadOnly="True" />
                </DataGrid.Columns>
            </DataGrid>
        </StackPanel>
    </GroupBox>
    <GroupBox Header="Ações" Grid.Row="1" >
        <StackPanel Orientation="Horizontal" Margin="10" HorizontalAlignment="Right">
            <Button Content="Atualizar" Height="25" HorizontalAlignment="Left" Name="btnAtualizar" Width="100" Margin="5" Click="btnAtualizar_Click"/>
            <Button Content="Sair" Height="25" HorizontalAlignment="Left" Name="btnSair" Width="100" Margin="5" Click="btnSair_Click" />
        </StackPanel>
    </GroupBox>
</Grid>