Please help me resolve align control problem

Hi all.
Today i've create a page with layout like as below :

1. I have a StackLayout with these options :

           Orientation = StackOrientation.Horizontal,
           HorizontalOptions = LayoutOptions.FillAndExpand,
           Spacing = 0
   

2. Inside StackLayout, i add a Entry and an image. I try align image to right with fixed width : 20, and Entry must auto-size to fill the rest of width. But it didn't work.
   With Entry, i set HorizontalOptions = LayoutOptions.StartAndExpand and image, i set HorizontalOptions = LayoutOptions.EndAndExpand.
   But when i run application, width of the entry just get 1/2 width of stacklayout, and dont fill the rest.

   Pls help me resolve this problem.
   Sorry if my english is not good.
   Thank for your support.