I was in the exact same position as you two years ago except I went on to IB not A-Levels. At this point all you can really do is try to move on and make sure you don't make the same mistakes later in life. Just use this as a motivator for next time you're taking exams, remember the feeling you got when you knew you didn't do enough and ensure you don't feel like that again, take A-levels as a fresh start.
With regards for unis I think Oxbridge are the only ones I ever came across that wanted specific numbers of A* GCSEs so LSE, UCL and most other places are still viable options as long as you're maths and english grades are up to scratch (and your foreign language grade for UCL) which they seem to be.
If you knuckle down over the next two years then you can definitely get the grades you need for those unis. For UCL and LSE you're taking the right subjects to get in by choosing Economics and Maths (LSE also says it's more lenient because you're taking further maths). If you're really doubting yourself with Physics then it's probably not too late to change to another science or even to german/english instead of worrying about how you can get through the next two years.
As for everyone else getting all A*s trust me nobody will care about that by christmas, my year got the highest grades my school had ever seen and nobody has mentioned or discussed it since October of first year. I was surrounded by people who got all A*s when I knew I could've done better, it's inevitable that you'll beat yourself up about it but the more you do that the harder it is to move forward (plus you don't even know what you got yet). Bad GCSEs aren't the end of the world and you can still get to UCL and LSE if you make sure you're not in this position of regret again, trust me.
For now: you have two months until results day use that to unwind before school restarts, go out with your friends, if they start talking about exams steer the conversation away or just excuse yourself, they'll get the hint and eventually everyone will move on. Try to absorb yourself in learning a new skill bake, brush up on you German, learn to code or play an instrument. Alternatively unplug from the technology (at this point lurking on TSR is probably not a good idea) and go camping with friends or catch up on your reading or go sightseeing in your own town, do anything (anything at all) that isn't to do with exams. If you're like me then I'm sure my this point your textbooks, notes and past paper are everywhere - now is the perfect time to organise and tidy away, get them out of sight (even putting them in a cupboard helps) being surrounded by revision you didn't do is never helpful.
Hope this helps, feel free to DM me if you're struggling