There absolutely is room for creativity within the bounds of testable questions. Clinical psychology is a scientific field (we use the scientific method to systematically test hypotheses), so most papers are research reports. However, researchers also sometimes write theoretical papers in which they just discuss various psychological phenomena or put forth creative new theories that might or might not be testable. A theory that is not testable obviously will never have empirical support. What both "types" of research papers have in common is, as someone mentioned above, a comprehensive grasp of the existing literature and evidence so that the new theory or the new study builds on prior knowledge.
You are in a great position to start building your knowledge base in the topics that interest you. This is one of the most time-consuming and challenging tasks for new graduate students, as many are starting at the beginning, and there is so much to read, and you have a big head start! If I were you, I would start now with conducting lit searches and reading and annotating literature. There are several free citation managers that allow you to store, organize, and annotate papers/citations, and I assume your CC has access to PsycInfo and/or Pubmed, depending on your interests?
I also frequently recommend the book "What Psychology Majors Could (and Should) Be Doing: An Informal Guide to Research Experience and Professional Skills" by Silvia, Delaney, and Marcovitch. "Psychology majors" could be replaced by "people at any level who are interested in preparing for future application to PhD programs in psychology". The book focuses on preparation for PhD programs in any area of psychology, not just clinical, but I think it really gives great tips and helps students stop worrying that they're missing some essential step.
Edited to answer original question: It is challenging to narrow down interests. In the beginning I was interested in several broad (and related) topics. I started reading and taking relevant classes (more reading than classes), and from that broad foundation was able to naturally identify and focus on narrower subtopics. I have also changed research interests at several points, and one of my favorite things about research is the ability to shift focus as interests change. Of course you dont want to bounce around from topic to topic, but there are certain points in training when making changes is easier. For example, I changed subtopics between my enroute masters degree and my doctoral dissertation. In your case, you might seek out brief research experiences in several different labs before choosing one as a primary undergraduate research experience.
Your enthusiasm is really great, and I wish you the best!