Hi there!
Learning the rest of the syllabus might not be a good idea. It’s worth bearing in mind that not everyone at interview will have covered all of the topics (so questions might be tailored according to what you know rather than being set questions) and that it might mean you’re bored during your lessons
I also don’t agree with much of what the above poster said. The department covers a wide range of topics within chemistry, and you aren’t tied to your college for your fourth year research project supervisor - they can’t look to their own research expectations either since it’s that far in advance! Knowledge of legal issues is much less important than your ability to think through chemical problems in interview. And the interviews are academic, so while you should definitely be able to talk about whatever you’ve written about your personal statement in depth, doing this in and of itself as a separate thing isn’t something that would be helpful in an interview scenario
Instead, maybe try looking into things that extend beyond the syllabus? The C3L6 and Chemistry Olympiad questions are fun, and often start with something related to content you know and then move beyond that. The format is very different to an Oxford interview, but they have that in common. The C3L6 papers are for Year 12s, so may be more appropriate at this stage. The NRICH website for maths also has a chemistry section, which has related mathematical problems, and the royal society of chemistry has resources called ‘chemistry for the gifted and talented’ which are quite fun and look at topics and models in more depth
Hopefully that’s given you some things to do, and if you work through them then I’m happy to recommend other things as well!