Yes, your response is not so different from that of native English speakers. "What's up?" means exactly the same thing as "what's new?", so the correct response is to report whatever new events are going on in your life, or, more often, to answer "not much"--or even to do a combination of both. For example, A: "What's up?'' B: "Not much. I just got home from work." That's a pretty standard type of interaction. To answer with another question is fine, since "What's up?" is only the smallest bit different (a little less formal) than "Hello.''