This happens occasionally. If you really have a “flair for languages”, you may prefer to join a higher-level class, even if you haven’t completed all the material in between. Some people are happy to study certain points themselves to fill in the gaps; they take the course not so much to understand the grammar and so on as to practise using the language in real life. Alternatively, the teacher can suggest additional material that you can work through to supplement what you are covering in class.