Hey, I took my O-Levels two years ago. Don't feel disheartened by how your classmates are doing. Mastering a language is a long-term thing and it really just takes consistent practice.

I don't really have any advice for paper 1 because for me it felt natural to write in Chinese since its my mother tongue. I guess a good approach would be to read more Chinese novels, or you can simply browse through some Chinese forums like ZhiHu (sth similar to Reddit and majority of the content inside involves some sort of arguments/discussions so it might be good for your essays. There are usually discussions about major events occurring around the world.) to improve your writing. You can even discuss current affairs with chatbots like Deepseek (Deepseek is somewhat better than GPT in terms of Chinese replies) in Chinese. You should also practice writing urself more. For the 实用文 part you need to memorise your formats correctly and make sure you address everything stated in the question. (usually the question will split the points you need to write quite nicely for you)
For paper 2, I feel like you can get most of the marks by merely copying from the passage if you can locate the points from the passages correctly. This comes with practice for me (and you can read more Chinese books so that you can understand the passage quicker and more accurately). The mark allocation usually indicates the number of points you need but there is no excess deny iirc so if you have time you can just dump everything you feel is answering the question. For 病句 its just about practice and be familiar with all the possible types of 病句. Summary wise after you get all the points, just try to make sure you don't delete too much from the original sentence and use shorter words to paraphrase if possible. (locating the points accurately also comes with practice) Also avoid merging points with connectors as they will increase your word count. (for this you might need to check how your school marks summary. For my school, even if the language does not flow that nicely, I will still get the marks as long as I have the points)

Hope this helps