You shouldn't create a separate file in your folder "feeds". The file will be created and named automatically by googlefeeder identical to the filename specified therein.
Example:
$OutFile = "../feeds/items.txt"; //"CHANGEME-full-path-to-file-with-777-dir-and-file-permissions-your-outfile.txt";
$destination_file = "items.txt"; //"CHANGEME-filename-to-upload-to-google.txt" ;
Nothing more required :thumbsup: