Will LSE & UCL accept me

Your grades are fine (amazing even since you go to an underperforming school). Most of the people getting all 9s go to private schools/grammar schools so don't be put off by them. I'm also an econ applicant (though I applied for straight econ at UCL and didn't apply to LSE) and I can say I don't have anywhere near as many supercurriculars as you 😅. You should just apply, no point swapping for somewhere not as good when you have a chance at one of these 2. They're just 2 of 5 choices.

but the thing is, i think my personal statement - it was well written, but definitely not as good as it couldve been, altought included all of them super curriculars there. And im worrying wether for maths with econ at ucl would require a heavy focus of maths on the ps, because i really didnt write much about it i mainly just wrote about financial models and things like that - my whole ps was practically the crossover for maths and econ, which i dont even know if it will work for lse

You are really overthinking this. Just apply anyway...

okay, where else did you apply?

Did you do TMUA?

Bath, Warwick, Bristol, Birmingham (offers from the last 3 so far)
No one can really tell you your chances. Some people with 4 A*s get rejected, whilst others that just meet the minimum requirement of A*AA get accepted. You cannot base your chances off grades alone. Admittedly your yes your GCSEs probably are a bit on the lower side for LSE, but they consider them in the context of your school so you should be fine. They value the personal statement quite a lot and you have loads of supercurriculars
Obviously it's up to you, but I really think you should just apply anyway. The worst that will happen is rejection and as long as your other 3 choices are bit safer you will still get an offer from somewhere. If you decide to swap then you might wonder later on if you would've got in if you applied. Good luck with whatever you decide
Btw just out of curiosity, where would you switch to if you decided to swap?