I don't want to do more than my job description says
Does your boss tell you to do other things?
Yes. He wants me to do things outside of the job description.
If what is requested of you is blatantly outside of your job responsibility then you should give HR a call. Either they need to increase your compensation or they need to speak with you boss about this. There is absolutely no reason to make you do things that you didn't sign up for.
No, HR always side with the boss. I can't depend on them.
Then maybe it is time to look for another job. It is not okay that they want you to do more work than you signed up for.