Hi! Grade 9 in Edexcel Chem over here- I think it's not the end of the world, and it's unlikely to make too much difference if you didn't make many other mistakes. It depends what the question was out of, and what else it was asking- You could still get partial credit on questions worth more than 2 I think if the question was also asking you to explain why, for example, and you gave a good explanation for why it would have ended up on the cathode, but called it the 'anode', you might still get 2 out of 3 marks, for example.
Congratulations on completing the exam, and best of luck for any remaining tests!