Most of the error messages are self-explanatory and can be easily fixed.
Your mimetype file contains a linebreak character at the end that needs to be deleted and the file reference in the
<guide> section of your package.opf file is missing the full path. You'll need to change it:
From: <reference type="cover" title="Cover Image" href="cover.xml"/>
To: <reference type="cover" title="Cover Image" href="
xhtml/cover.xml"/>
To implement these changes, change the file extension from .epub to .zip and then extract all files. (If you still have the original project folder you can of course update the files there.)
Then use
epubzip (OS X) or
epubpack (Windows) to re-create the .epub file.