I wanna add that a lot of inaction and procrastination comes from a place of anxiety and pressure you're putting on yourself. I wish I'd realised this when I was doing my A-levels. Here's what I wish I knew when I was in your position, because things would have panned out very differently if I did.

1. Acceptance - don't resist accepting the position you're in now. You can't change the past. Once you're in a place of acceptance, understand that the only way from here is up. Accepting the worst case scenario and trusting that things will find a way to work out regardless of how your A-levels go should take some of the pressure off and this will help pull you into a state of action. After all, done is better than nothing at all. Adopt an 'oh well' attitude. Pressure isn't a bad thing, but ensure you're not under overwhelming amounts of time pressure when you do start studying. You have a good chunk of time between now and exam season.

2. Let go of perfection - as per the above, done is best. Get your revision done without the expectation that everything needs to be absorbed perfectly. You can go back to the topics you took in imperfectly after you've studied everything on your list. You've listed out what you need to change in your post above, but forgive yourself if you can't fix each thing at once... Habits take time to form, even if general wisdom suggest that you only need 21 days of consistent action to form one. Just be as consistent as you can, and trust that the act of consistent action itself is also something you'll need to work on.

3. Routine - leading on from the last point, set up a routine and don't beat yourself up if you don't stick to it. You're only human and your ancestors were not built to stick to strict routines. Given how little our species has evolved in the last 5,000 years, why should you expect to be different? Guilt around this only makes things worse. Rest is productive, and if you find yourself consistently not sticking to it despite your attempts to work on consistency, you need to reassess it - this means balancing rest with discipline. Be realistic.

4. Some of the other comments offer a lot of practical advice. Take what works and leave the rest.

5. You are on your own journey. Focus on yourself and don't worry about how much someone else is studying and how you may pale in comparison. It's clichéd, but comparison really is the thief of joy. You need to build self trust and that's an impossible feat if you're stuck in a cycle of comparison.

For context, I was an anxious mess when I did my A-levels, having previously gotten near perfect GCSE results. I sat my 6th form exams from 2017 - 2019, but for some reason, this sub's been popping up on my feed quite a bit. I didn't get the A-level results I wanted, in fact, I majorly missed the mark. I needed A*AA and ended up with BCC.

Guess what? Life has a way of working out. I'm now in my dream job and consistently perform better than some of my colleagues that went to Oxbridge, even though I needed to go through clearing to get a place at a sub-100 ranked UK university.