Should I ask for co-authorship as an undergrad student? I was assigned a research topic for one of my psych classes this term. I designed the study, collected and analyzed data and then wrote a paper. After I presented my paper to my professor, she was very excited and said this paper was publishable. She would definitely run follow-up studies on this topic. I then offered to join her team to run this study and she agreed. 

Now I am not sure if I am only participating as a volunteer research assistant or as a co-researcher for this project, considering the research topic is not my original idea. I just designed the study, ran it and received significant results. 

Should I ask for clarification on my role at the upcoming meeting with my prof ? If so, how should I approach? I don't want to appear too aggressive.
If you have conducted the pilot study and are also part of the follow-up team expanding it into a full publishable study, then you should definitely be invited to help write and be an author of the paper.

This should also be an easy and uncontroversial decision for your professor.  It's also fine and in fact good to get that clarification explicitly now.  You can just ask something like: 


  I'm excited about helping turn this project into a paper.  Am I right in thinking this means I will be an author of the paper as well?


This is not a hard question, so if your professor says anything other than "yes," (possibly with appropriate caveats about you actually sticking with the project) then you should be concerned.