stretch my buttons in a TopAppBar

[Imen]

Hi,
I am developping a universal application in visual studio 2015 Community,but I have a problem in stretching my 3 buttons when I test my application on local PC or the windows phone emulator,this what I get whith my code:

<CommandBar Height="51" >
            <CommandBar.Content>
                <Grid>
                    <StackPanel>
                        <Image x:Name="image1" Height="37" Width="127" Margin="41,10,-168,-50" Source="images/name.png" RenderTransformOrigin="0.487,0.82"/>
                        <Image x:Name="image" Height="49" Width="39" Margin="1,0,-40,-50" Source="images/icon.png"/>
                    </StackPanel>
                    <StackPanel>
                        <Button  Height="49" Margin="0,0,-244,0" Width="35" HorizontalAlignment="Right" VerticalAlignment="Stretch">
                            <Button.Content>
                                <Image Source="images/home.png" Margin="-9,0.333,-9,-0.667"/>
                            </Button.Content>
                        </Button>
                    </StackPanel>
                    <StackPanel>
                        <Button  Height="49" Margin="0,0,-280,0" Width="35" HorizontalAlignment="Right" VerticalAlignment="Stretch">
                            <Image Source="images/search.png" Margin="-9,0.333,-9,-0.667"/>
                        </Button>
                    </StackPanel>
                    <StackPanel>
                        <Button  Height="49" Margin="0,0,-315,0" Width="35" HorizontalAlignment="Right" VerticalAlignment="Stretch">
                            <Image Source="images/profil.png" Margin="-9,0.333,-9,-0.667"/>
                        </Button>
                    </StackPanel>
                </Grid>

            </CommandBar.Content>

this what I want to get :(attach file)

thanks for help