Получил работу, используя вместо этого:
<?xml version="1.0" encoding="UTF-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="RoseySports.Login_Page">
<AbsoluteLayout VerticalOptions="FillAndExpand" HorizontalOptions="FillAndExpand">
<Image AbsoluteLayout.LayoutFlags="All" AbsoluteLayout.LayoutBounds="0, 0, 1, 1"
Source="background.jpg" Aspect="AspectFill"/>
<ScrollView AbsoluteLayout.LayoutFlags="All" AbsoluteLayout.LayoutBounds="0, 0, 1, 1">
<StackLayout Padding="0, 40, 0, 0" HorizontalOptions="Center" VerticalOptions="Center" Grid.Column="0" Grid.Row="0">
<Label Text="Email" HorizontalOptions="Center" TextColor="White"/>
<Entry Keyboard="Email" WidthRequest="300" x:Name="email"/>
<Label Text="Password" HorizontalOptions="Center" TextColor="White"/>
<Entry IsPassword="true" WidthRequest="300" x:Name="password"/>
<Button Text="Login" x:Name="login" Clicked="Handle_Clicked" TextColor="Navy"/>
</StackLayout>
</ScrollView>
</AbsoluteLayout>
</ContentPage>