Putting your Root Grid or your LongListSelector Marging work?
Margin="0,0,0,75"
Like:
<Grid x:Name="ContentPanel" Grid.Row="1" Margin="0,0,0,75" />
Greetings!
UPDATE
I was searching now a little bit on google and I found this article. I recommend to read it.
In this article I saw that the LongListSelector has a ListFooterTemplate, so you can set a footer and it will work.
<DataTemplate x:Key="citiesListFooter">
<Border Background="White" Opacity="0.2" Height="70">
<TextBlock Text="Cities Footer" VerticalAlignment="Center" HorizontalAlignment="Center" Foreground="Black"/>
</Border>
</DataTemplate>
put it in your MainPage.Resource and after in your LongListSelector put this line of code:
ListFooterTemplate="{StaticResource citiesListFooter}" Margin="1,0,-1,0"/>
This example is from the link I give you above. Hope helps.
greetings!