facing problem in aalignment of stack panel

Question

<Window x:Class="SlidingChart.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:charting="clr-namespace:System.Windows.Controls.DataVisualization.Charting;assembly=System.Windows.Controls.DataVisualization.Toolkit"
        xmlns:ref="clr-namespace:System.Windows.Controls.DataVisualization;assembly=System.Windows.Controls.DataVisualization.Toolkit"
        xmlns:annonation="clr-namespace:System.ComponentModel.DataAnnotations.Schema;assembly=System.ComponentModel.DataAnnotations"
        Title="MainWindow" Height="436" Width="700" Loaded="Window_Loaded_1">
    <Grid>
        <StackPanel Margin="0,0,196,0">
            <charting:Chart Name="parentchart"  Height="393" Loaded="parentchart_Loaded">
                <charting:Chart.Axes>
                
                    <charting:LinearAxis Orientation="X"   x:Name="orty"  Maximum="{Binding Path=Text, ElementName=txtx,Mode=TwoWay}" Title="Ledmodule operating (mA)" ShowGridLines="True"> 
                    </charting:LinearAxis>
                    <!--<charting:LinearAxis Name="ycordinate" Orientation="Y"  Maximum="{Binding Path=Text, ElementName=txty, Mode=TwoWay}" Title="operating Current(mA)"   Interval="40" ShowGridLines="True"></charting:LinearAxis>-->
                </charting:Chart.Axes>
                <charting:LineSeries Name="charts" ItemsSource="{Binding UpdateSourceTrigger=PropertyChanged}" DependentValuePath="Value" IndependentValuePath="Key" IsSelectionEnabled="True"   >
                   
                </charting:LineSeries>
            </charting:Chart>
        </StackPanel>
        <StackPanel   HorizontalAlignment="Left">
        <GroupBox Header="do changes here"    Margin="501,20,0,0" VerticalAlignment="Top" Height="376" Width="181">
                <StackPanel>
                    <TextBox HorizontalAlignment="Left"  Name="txtx"  TextWrapping="Wrap"  Width="126" Margin="0,0,0,178"></TextBox>
                <TextBox Name="txty"    VerticalAlignment="Top"></TextBox>
                <ListBox Height="23" Name="cmb"></ListBox>
                <!--<TextBlock ScrollViewer.VerticalScrollBarVisibility="Visible"  TextWrapping="Wrap" Name="cmb" Text="TextBlock"/>-->
                <TextBox Height="23" BorderThickness="2" TextWrapping="Wrap" Name="txtxvalue"  TextChanged="txtxvalue_TextChanged"/>
                <TextBox Height="23" TextWrapping="Wrap" Name="txtyvalue" />
                <Button Content="Button" Click="Button_Click_1"/>
                </StackPanel>
            </GroupBox>

        </StackPanel>
    </Grid>
</Window>


when i am streching my screen group box is fixed.
when clicking on the maximize button of window they overlap each other