Publish audio + image to Youtube, but I have black borders. Why?

[defaultprxlbf0whr90]

I'm new at Premiere.  I just want to do a simple task, combine an audio track with a single square image, and then export/publish it to Youtube. But when I do this, the image doesn't fully fill the youtube display.   The image is scaled so that the Youtube video playback controls don't overlay it.   I get a black border around it.   I have right clicked and selected "Scale to Frame", as otherwise Premier's display similarly shows a large black border.  When I select that, Premier then scales the image it so that it full fills the height of the display.   But this has no effect on what is uploaded to Youtube.   I thought what I see on the Premier display would be duplicated when I selected to Publish to Video.   But obviously not.

I must be doing it too simple.   Maybe I need to save the project?   Or define the image size?    I was assuming what I see on the Premier display would be duplicated on Youtube publish, but obviously not.   Thanks for helping a clueless person. - Mark 

[Richard van den Boogaard]

Please include a few screen shots of what it is you are doing, for clarity purposes.

However, based on your description, there seems to be a mismatch between your source footage and the sequence you're creating and how the result is shown on YouTube.

As far as I know, YouTube mainly works with 16:9 footage, not 9:16 or 1:1: https://support.google.com/youtube/answer/6375112