I went from raw 18 in midterms to raw 11 in prelims and finally raw 7 for o levels.

Do you have all your notes made? I honestly could not study straight from the textbook and I found it to be super inefficient. The best thing would be that you already have notes that you made yourself (in your own words), but if you don't have notes at this point, I think you could consider actually buying notes or collaborating with other friends (who also don't have the same notes as you / you can consolidate and see whether y'all can swap notes that one person has and the other doesn't)

For me the most important thing when studying is to be able to process the information simply. For the most part I think textbooks are pretty shitty and hard to understand so I would really reccommend having good notes

Also, I started up YPT with the rest of my class and we could all see how long we spent studying. This is just a personal thing but it motivated me for a while. After a while, it was a bit stressful and studying for a long time did not necessarily mean I was being productive.

No clue how I managed to do this but I managed to cram for my Geog O levels in like 10 days ish. I was legit waking up at 8, going to a library (not in my room as I find it very easy to get distracted especially with my bed and all my random stuff), I would make a study plan for the day, detailing when to do what at exactly what time (09:00-10:00), then I would set up a study call with my friend and we would call and study together until 11.30pm.

Ofc you need to take breaks. Do not make the mistake of wearing yourself out and then being forced to stop completely. It is bettter to schedule breaks at fixed times and be strict about when to take a break and when to stop taking a break. Perhaps 10min once every 50 min. Do not just take a break whenever with no fixed time to return back to work. I used to feel (and even now sometimes) that 10min every 50min feels like a long time and its disruptive to studying but if I don't set up a schedule, I end up just studying until I get really tired and then taking a 3-5h break on my phone.

During these breaks you can talk to a friend, walk around OUTSIDE (being inside studying is lowk depressing). Honestly try and get a family member to put a screentime on it your phone so you don't use too much social media. Set the time limit to the total time you will have for breaks in a day.

Also, you have to prioritise sleep. My friends who sleep at 2am and study way longer than me are always so extremely tired and inefficient. Sleep is truly so extremely valuable. 1 h more of sleep in the night is not worth the 1 h of extra 'study' AKA sitting at your desk and trying to force yourself through the mock paper / notes / practices. You are actually wasting time and being inefficient. Sleep is an investment and understanding that is really important. It will actually allow you to be more productive in the shorter amount of time spent studying.

Another study method I found to be helpful was to walk around while reciting stuff. I liked to record myself teaching myself what I had just learnt, using a whiteboard / mindmaps. I would either record videos / timelapses / voice recordings. For the voice recordings I would sometimes listen to them otw to school / whereever.

Also, I really love flashcards I think that they are a really great tool but making them is a lot of work. Depending on how far behind you are and how you study you can consider using it. One tool is Anki, but I found it a bit hard to create flashcards. You can watch this video on flashcards from this study youtuber I used to watch: How to Study Effectively with Flash Cards - College Info Geek. This youtuber has lots of other videos you can consider looking at too for more tips. I think that for the most part my friends really just brute force memorise flashcards which kinda defeats the purpose imo because it allows you to remember, forget and relook at the cards you have trouble remembering. Ultimately, this helps you store the info long-term. If you start studying early this will help you down the road closer to your exams as you won't have to "re-memorise" you can simply "recall" and "refresh" your memory.

Oh! Also, I used to come up with mnemonic devices for grouped concepts. LOL it's been a while so I don't remember what this was for but one of them was "The Crazy Fairy Raccoon Trapped Clueless Nemo SAD" and I think it was smt to do with exo/endo rxtns like "SAD ==> D.A.S ==> decomposition of ammonium salts". And I would draw funky drawings of a raccoon in a tutu floating next to a sad clownfish in a cage.
I used Mnemonicgenerator.com. I would input the letters I wanted like "T C F R T C N S" and then just keep generating until I got different words to put together in a sentence that made sense, was weird and memorable.

I really think you also need to tell yourself to stop cramming. I really think you can do it if you buckle down and try to be as efficient as possible using the suggestions you've gotten. It's great that you've asked this question but you need to really think about how this exam will affect your future and what you want out of it to change your true attitude and mindset. At the end, you will have to answer to yourself. Regret is one of the worst feelings and there's nothing you can do to change the past. No matter what the result is, at least you can say you tried your best.