You must have added the code in the wrong spot, or maybe you left out something? Anytime you add code, it must be after the first . I just tested the above code myself and it worked fine for me. Did you change anything? If you remove a comma, semicolon, etc it will cause an error with php. I would copy and paste the code again exactly as it is to make sure it works, and then edit the words Leave a Comment.
I always recommend making PHP edits with an external editor and an FTP program. By using FTP externally, if you make a mistake (missing comma, semicolon, etc) you can undo it and resave from within the program….then the error will go away. If you make a mistake with the WP admin editor, then it becomes difficult to get back since the error notice takes down the entire site.
If you can’t go backwards (using your “back” button) and resave, then you’ll probably have to contact your host and have them revert back to a saved point…..you could also just replace the functions.php file with an FTP program and the error would go away immediately.
It is highly recommended to use and get familiar with an FTP program when editing PHP files. I recommend Filezilla, and depending on whether you have Mac or Pc, you can search for a php editor. It will be much easier to make edits to your css and other files as well.