I didn't study German at A level but did do French so I'll give some general advice.
Ensure you're familiar with all topical vocab (quizlet is a great site to use - as you do) and grammar rules. For Speaking I recommend you have some topical facts for the photo card so you can support your opinions and show an understanding of German culture. You can also implement set sophisticated phrases into your speaking and do the same with essay phrases also.
I also did Biology and Chemistry A level too but never met an aspiring medic who also did a language alongside those subjects!
Wish you all the best with your studies and application.