When you get the html for the embedded view, part of the code should say width="100%". This will make the embedded view take up 100% of the width that is available to it. However, that is not the same as taking up 100% of the screen. If the parent html container only as a portion of the screen, then the embedded view can only expand that wide. (There are workarounds, but they require a deeper understanding of web page design.)
I suggest that you look at the rest of the web page that contains the embedded view and see if you can make adjustments there to allow the parent container for the embedded view to take up more width.
If this answer gives you enough information to solve your problem, could you please mark this post as the solution?
If not, could you please give a bit more details on your use case and a larger screen capture?