mainUserControl.xaml

<UserControl x:Class="TestApp.mainUserControl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:SaiData.TestApp"
             mc:Ignorable="d" 
             >
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="5*"/>
            <ColumnDefinition Width="43*"/>
        </Grid.ColumnDefinitions>
        <StackPanel Name="panel1" Margin="18.971,24,24,0" Grid.Column="1">

        </StackPanel>
    </Grid>
</UserControl>