Biophysics is a broad and interdisciplinary field with contributors from various disciplines. It's driven largely by problems in biology and the people trying to solve them bring different tools to the table. A biologist who wants to model the diffusion of a certain drug through a tissue might contact a physicist who has experience in that area rather than re-inventing the wheel. Or if she or he wants to develop a new way of counting certain types of cells drawn in a sample she or he might contact a physicist who can figure out how to light scatters differently through the different cells and develop a system for measuring that. Biologists and physicists aren't exclusive to the group either. You have chemists, engineers, mathematicians, neuroscientists, who also make significant and even leading contributions to the field.
Going into undergraduate studies is a difficult time to know what kinds of problems you would really enjoy working on because most people don't have a lot of experience at that age to make an informed decision. That's why it's usually a good idea to avoid too much specialization too early.
If you're unsure of even a decision between physics and biology, you might want to start by enrolling a general science program and take a first year or study that would qualify you to go either route. Spend that first year concentrating on your courses, but also talking with senior students, and even graduate students if you can. Then make the decision as you go into your second year.