Note that this could be a problematic proposition because once the script has been run the file is there. How do you set apart the file that has already been there from the first run from the file to be created by the second run, hmm?
This is most probably because zip doesn't write to a file named Ubuntu_Documents.zip". Perhaps your zip-file has some other name (i suppose, from the commandline, "test.zip") and you would have to reflect this name in the cp -command.
Furthermore, are you sure you want to name the file "whatever.txt"?? A file ending in .txt is supposed to be plainly readable text and .zip-files aren't exactly that.