Does doing well in one subject mean you should pursue that field of study?

You cannot use a single result to treat being good at something and enjoying it as the same thing. Understanding a subject and doing well on a test show one kind of ability. Whether you enjoy studying it further and want to pursue that direction still requires exploration.

In junior high, I once received the highest score in my class in physical science. I could understand the teacher's theories and formulas and knew how to apply them. At the time, I assumed I was strong in science and suited to chemical engineering. Only after actually studying it did I discover that understanding a subject did not mean I liked that field.

Looking back at this experience, doing well on one occasion does not settle your future direction. Along with your abilities, you need to understand your interests. If you do not yet know what further study involves, find out more rather than letting one grade decide your whole path.