I had many bad French teachers too but some useful websites are
Memrise (for vocabulary)
Languagesonline (Tenses, agreements)
Kerboodle, ik not all schools will have this tho but it was good for listening and stuff
Also i would recommend this book )https://www.amazon.co.uk/gp/product/...?ie=UTF8&psc=1) pretty much covers all the bases when it comes to the skills needed. This one is mainly grammar and translation but also highly recommended (https://www.amazon.co.uk/gp/product/...?ie=UTF8&psc=1).
Great question and don't worry about it. You have still got time and you can study it and get a top grade with some help. Online courses which go through the topics and give model top grade answers are superb because they literally help you understand what you are missing in your knowledge and also what is required for the top grades. They helped me when I did my GCSEs at least!!
Not only this, but the course will help you significantly for 2 exams: your SPEAKING and WRITING, which is superb.
A course which I recommend for GCSE french is:
go to >>> bytesofintelligence dot co dot uk and get their French Course (click on Buy Now at the bottom). I think you will find it very useful.
Trust me - it is worth it. For literally 10 pounds, you cannot spend the money in a better way! It will help you for the whole GCSE course and goes through all the topics and suggestions with it.
Hope this helps!!