Image in scrollview is not scrolling in WPF xamarin.forms

I am trying for Zoom in-Zoom out for an image in WPF using xamarin.forms. The following is my code for zoom functionalities.

 <ContentPage.Content>
        <ScrollView>
            <StackLayout>
                <Image x:Name="ImageToDisplay"
               HorizontalOptions="Center"
                VerticalOptions="Center"
                Aspect="AspectFill" >
                </Image>
                <StackLayout Orientation="Horizontal" Grid.Row="1" HorizontalOptions="CenterAndExpand">
                    <Button Text="ZoomOut" Clicked="ZoomOut"/>
                    <Button Text="ZoomIn" Clicked="ZoomIn"/>
                </StackLayout>
            </StackLayout>
        </ScrollView>
    </ContentPage.Content>

private void ZoomIn(object sender, EventArgs e)
{
var currentScale = ImageToDisplay.Scale;

    if(currentScale>=1 && currentScale < 5)
    {
        ImageToDisplay.Scale = currentScale + 0.25;
    }
}

private void ZoomOut(object sender, EventArgs e)
{
    var currentScale = ImageToDisplay.Scale;

    if (currentScale >= 1 && currentScale < 5)
    {
        ImageToDisplay.Scale = currentScale - 0.25;
    }
}`

I can able to zoom in and zoom out but the problem is, when the image is zoomed to max it is not scrolling.

How to make it to be worked?