How can I make controls in WPF stretch to fill available width when HorizontalAlignment and HorizontalContentAlignment don't work?

Question

I'm trying to make a simple WPF app that has sections that fill the available width. Despite trying various ways of stretching the width of elements, containers, and children, nothing is working and I can't figure out why.

Another question said to use uniformgrid which worked well EXCEPT that it set the height of all the elements uniformly which was definitely not what I wanted. I want all of the sections to look like the one in the picture - filled width, height auto based on the content. Here's the basic setup:

<Window x:Class="A_Customizer.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:A_Customizer"
        mc:Ignorable="d"
        Title="MainWindow"
        Background="#FF2B2B2B"
        Width="800"
        >
    <Window.Resources>
        <Style TargetType="{x:Type Button}">
            <Style.Triggers>
                <Trigger Property="IsMouseOver" Value="True">
                    <Setter Property="Cursor" Value="Hand"/>
                </Trigger>
            </Style.Triggers>
        </Style>
        <Style TargetType="{x:Type CheckBox}">
            <Style.Triggers>
                <Trigger Property="IsMouseOver" Value="True">
                    <Setter Property="Cursor" Value="Hand"/>
                </Trigger>
            </Style.Triggers>
        </Style>

    </Window.Resources>
    <Grid Name="mainApp" >

        <Grid.RowDefinitions>
            <RowDefinition Height="30"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>

        <WrapPanel Grid.Row="0" >
            <Button ToolTip="Click to apply the below settings to this Jumpbox" Click="ApplyCustomizations">Customize</Button>
        </WrapPanel>

        <ScrollViewer Grid.Row="1">

            <WrapPanel HorizontalAlignment="Stretch" >
                <GroupBox
                    Background="#FFE2E2E2"
                    BorderBrush="#FF7F7F7F"
                    Margin="10,10,10,10"
                    Name="pathsBox"
                    HorizontalContentAlignment="Stretch"
                    HorizontalAlignment="Stretch"
                    >
                    <GroupBox.Header>
                        <Border Background="#FFAFAFAF" CornerRadius="3">
                            <Label FontWeight="Bold">Key Paths</Label>
                        </Border>
                    </GroupBox.Header>

                    <StackPanel HorizontalAlignment="Stretch">
                        <Grid Margin="0,10,0,0">
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="*"/>
                                <ColumnDefinition Width="50"/>
                            </Grid.ColumnDefinitions>

                            <TextBox Name="homeFolder" Grid.Column="0" HorizontalAlignment="Stretch"></TextBox>
                            <Button Grid.Column="1" Click="NewQuickPath" ToolTip="Change home folder">
                                <Image Source="images\add_folder.png" Height="25" Cursor="Hand"></Image>
                            </Button>
                        </Grid>

                        <TextBox Name="progFolder" Grid.Column="0" HorizontalAlignment="Stretch"></TextBox>
                    </StackPanel>

                </GroupBox>

                <GroupBox
                    Background="#FFE2E2E2"
                    BorderBrush="#FF7F7F7F"
                    Margin="10,10,10,10"
                    Name="quickBox"
                    Height="auto"
                    HorizontalContentAlignment="Stretch"
                    >
                    <GroupBox.Header>
                        <Border Background="#FFAFAFAF" CornerRadius="3">
                            <Label FontWeight="Bold">Quick Access Folders</Label>
                        </Border>
                    </GroupBox.Header>
            
                    <StackPanel HorizontalAlignment="Stretch">
                        <TextBlock TextWrapping="Wrap" Margin="15">
                            There are going to be folders you'll need to access frequently and keeping them pinned on top of the left menu in Explorer is helpful. 
                            Select here to add them to the list of folders restored with the "Customize" button. Click any folder to remove it.
                        </TextBlock>

                        <Border CornerRadius="3" Background="#FFF3C7C7" Margin="6" Visibility="Collapsed" Name="quickErr" Tag="err_box">
                            <TextBlock Tag="errMsg" Foreground="#FFFD3434" TextWrapping="Wrap" Margin="6" ></TextBlock>
                        </Border>

                        <UniformGrid Name="quickPathsArea" Columns="1">
                    
                        </UniformGrid>
                
                        <Grid Margin="0,10,0,0">
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="*"/>
                                <ColumnDefinition Width="50"/>
                            </Grid.ColumnDefinitions>

                            <TextBox  Grid.Column="0" HorizontalAlignment="Stretch"></TextBox>
                            <Button Grid.Column="1" Click="NewQuickPath" ToolTip="Add a new folder">
                                <Image Source="images\add_folder.png" Height="25" Cursor="Hand"></Image>
                            </Button>
                        </Grid>
                    </StackPanel>
                </GroupBox>     
</wrappanel>
</scrollviewer>
</grid>

Answer 1

StackPanel with Orientation="Vertical" (default value) instead of WrapPanel should work: it will allow each child element use full width and as much height as necessary