It depends on how much you enjoy the pain of studying each. Do you work hard at the thing you enjoy? Do you throw yourself at it with lots of energy and enthusiasm? Do you study outside of that thing, maybe talking to people who work in the field or reading books that are not on the syllabus. If you put a ton of energy and enthusiasm into it despite how exhausting that effort may be, then I'd stick with it. On the other hand, if it just comes easily to you and you're coasting through your classes and are doing well despite putting in no effort, then I would consider other routes. What's going to happen when the work gets hard? By the way, the work always gets hard. Michael Phelps didn't just wake up one day and find himself an Olympic athlete. He pushed himself constantly. His lungs burned. His muscles ached. He went to bed exhausted every day. But he loved it and had a special talent. So he worked as hard as he possibly could.
Also, why not both? I majored in business and psychology. Two seemingly disparate fields that I studied simply because I was interested. Now I work in marketing, which is a blend of the two. The worlds of computer science and biology have massive implications for the world and the world wants to read about and learn about those things. Maybe you can be someone who uses knowledge of both to help the CS and Biology worlds to connect with the larger world. Technologists and scientists are usually poor communicators. Maybe you can be that bridge?