Is there any way wrap a AutoWrapText correctly?

Hi all. Is there any way wrap a AutoWrapText correctly?
I am trying to apply a simple IM in my project, and trying to make it looks like Telegram. I am using RichTextBlock with true on Auto Warp Text, to contain text message, but get stuck on how to warp RichTextBlock correct with border or any image. I tried using GetSize to calculate size for border manually, but it seems the value returned by GetSize is not match with actual size. Thanks for any ideas!

Can you show us a picture of your widget so we get an idea of your border/image.

You can just reduce the width/height of your text box so it wrap in a smaller dimension than your background border/image.