Picture doesn´t fit ImageButton - xamarin.forms

Question

I want to write an app for Android with Xamarin.Forms and i want an ImageButton like in this question: How to make a Floating Action Button in Xamarin Forms
The problem is as soon as i set the Background of the Button the Image is not displayed correctly. The Button is on the upper left corner of the Image and the Image is super big. The Button is shown correctly.
This is my Xaml with the Button:
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:d="http://xamarin.com/schemas/2014/forms/design"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:android="http://schemas.android.com/apk/res/android"
mc:Ignorable="d"
x:Class="ASUE.Views.ItemsPage"
Title="AllItems"
x:Name="BrowseItemsPage">
<ContentPage.ToolbarItems>
<ToolbarItem Text="Archive" Clicked="Archive_Clicked"/>
</ContentPage.ToolbarItems>
<AbsoluteLayout>
<ScrollView AbsoluteLayout.LayoutFlags="All" AbsoluteLayout.LayoutBounds="0,0,1,1">
<StackLayout>
<ListView x:Name="ItemsListView"
ItemsSource="{Binding Items}"
VerticalOptions="FillAndExpand"
HasUnevenRows="true"
RefreshCommand="{Binding LoadItemsCommand}"
IsPullToRefreshEnabled="true"
IsRefreshing="{Binding IsBusy, Mode=OneWay}"
CachingStrategy="RecycleElement"
ItemSelected="OnItemSelected">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout Padding="10" BackgroundColor="{Binding BColor, FallbackValue='White'}">
<Label Text="{Binding Title}"
LineBreakMode="NoWrap"
Style="{DynamicResource ListItemTextStyle}"
FontSize="16" />
<Label Text="{Binding ActionTime}"
LineBreakMode="NoWrap"
Style="{DynamicResource ListItemDetailTextStyle}"
FontSize="13" />
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>
</ScrollView>
<ImageButton Source="add.png" AbsoluteLayout.LayoutFlags="PositionProportional" AbsoluteLayout.LayoutBounds=".95,.95,80,80" BackgroundColor="Transparent"/>
</AbsoluteLayout>
</ContentPage>
I expect the Image to be the same size as the Button
Update
I tried This
<ImageButton Source="add.png"
AbsoluteLayout.LayoutFlags="PositionProportional"
AbsoluteLayout.LayoutBounds=".1,.1,80,80"
BackgroundColor="Accent"
CornerRadius="80"/>
This
<ImageButton Source="add.png"
AbsoluteLayout.LayoutFlags="PositionProportional"
AbsoluteLayout.LayoutBounds=".1,.1,80,80"
BackgroundColor="Accent"
CornerRadius="80"
Padding="0,0,75,75"/>
This
<ImageButton Source="add.png"
AbsoluteLayout.LayoutFlags="PositionProportional"
AbsoluteLayout.LayoutBounds=".1,.1,80,80"/>
and This
<ImageButton Source="add.png"
AbsoluteLayout.LayoutFlags="PositionProportional"
AbsoluteLayout.LayoutBounds=".1,.1,80,80"
CornerRadius="80"/>

Answer 1

You need to set CornerRadius to have a circle button. You also need to set the Padding property to make your image smaller:
<ImageButton Source="add.png"
AbsoluteLayout.LayoutFlags="PositionProportional"
AbsoluteLayout.LayoutBounds=".95,.95,80,80"
CornerRadius="80"
Padding="15"
BackgroundColor="Accent"/>
where add.png is:
You can get it here: https://material.io/resources/icons/?search=add&icon=add&style=baseline
in black or white

Answer 2

i just limit its width and height like this,is it the effect you want ?:
<ImageButton Source="add.png"
HorizontalOptions="Center"
VerticalOptions="Center"
CornerRadius="25"
WidthRequest="50"
HeightRequest="50"
AbsoluteLayout.LayoutFlags="PositionProportional"
AbsoluteLayout.LayoutBounds=".95,.95,80,80"
BackgroundColor="Accent"/>

Answer 3

Thanks for all your help but nothing of this works sadly.
So i just made a normal button with the picture as ImageSource and resized the picture correctly to fit the button.