Hallo, please don't give up, the best thing I would advise you to do is do projects that you would really enjoy doing and then link them towards your theme, usually, they like a variety of media, artists, and styles so experiment and record within your portfolio. what helped me was writing down all the artists I wanted to cover, a good website is this one it has artists and themes:
https://theartyteacher.com/artists-themes/ For any annotations they like waffle but if you want to go in-depth look at precisely colour, setting, style, and artist, and explain what they mean in that artwork and why you or the artist had chosen to do this.
Fill up the page with lots of texture, annotations artwork, and anything! It goes a long way and can also create fun and if it links to your theme develop your book
your own work goes a long way although studies and copies are good, higher marks go to those who show they can derive their own ideas, photo shoots and contact sheets go a long way.
If you make any work you don't like keep it and write why you didn't like it and analyse what you tried doing. Taking pictures of your work in progress and planning is good.
Don't look to perfection if you are a perfectionist, even if its half complete but decent its enough, you can spend ages developing your art
Also if you still feel you don't have enough work, you can submit any sketchbooks you have done work in, one of my friends did this, and the other made a collage of old drawings. if you talk to your teacher you can submit books you've worked on in yr 9 if you consider them relevant or proud of
I would also say to communicate with your art teacher if you can for detailed advice, they can really help steer your work in the right direction and also give ideas. it's ok to be this level at this stage, I myself during covid was 7 weeks behind and caught up and got a grade 9, believe in yourself and enjoy the process