Help with Storyline Player Size

Here's what strikes me as odd:

• The image of your Player Properties shows the Modern Player selected, which is shown in the Preview area on the right. It has a dark background and the Modern buttons.
• The image of the previewed/published slide looks like it's using the Classic Player. It shows a light background and the Classic-style rectangular buttons. 

Perhaps, as AndrewBlemings-​ suggested, there's some sort of co related to an inserted template with different sizing and other properties. Or it might just be that the file got corrupted some other way. (See How to Fix Unexpected or Erratic Behavior)

Beyond that, troubleshooting is just guessing without seeing the file. Here are the best practices for uploading a .story file:

• Only include slides that are related to the problem.
• Be sure objects, layers, motion paths, and variables have meaningful names.
• If there is proprietary content, replace or delete it. For example, replace proprietary text with “ipsum lorem” text.

One more option: submit the case  to the staff.