Submitting a package for review puts a big burden on the reviewers and I would like to ease their work as much as possible.
However, there is currently no way to preview the contents of the package before it is actually published.
There used to be a way to preview it in the Asset Store Tool, but not now.
Furthermore, it would be nice if I could see the contents in the preview on the website.
When you use the upload function it opens a file browser and highlights the file it is uploading. You can use that to test and confirm that the package works correctly.
Also, you should post this in the private forum instead of the public one. You can get instructions on how to join in the Publisher Portal.