Wrong firm? What to do now...

Okay, so I am stuck in a kind of Dilemma and unsure of what to do.
I applied for mathematics, starting in fall 2018. I got offers from UCL and Glasgow and then firmed UCL and put Glasgow as insurance.
I thought I really wanted to go to London but upon consideration there are many reasons why Glasgow is better suited for me (cheaper, the degree is longer so less stressful, the city is not as busy as London etc etc...) Thinking about it I only put UCL because of prestige I think.. so I am convinced I want to go to Glasgow (Or at least not UCL)
Now I am not sure what to do because I have several options:

I took the IB exams two weeks ago and will get my results in the beginning of July. I could wait for results day and simply hope to miss my offer. I am unsure of my grades, the exams went well and my predicteds have been good year round. On the other hand UCL's offer is of course insanely high (40p with 7,7,6 at HL). I am very confident that I have met Glasgow's offer though, seeing at it is significantly lower (36p with 6,6,5 at HL)

Then I could try and switch firm and insurance now by trying to get both unis to agree to the switch. I have read that this works sometimes and I feel like there is a good chance this would work here too because UCL is very competitive and surely someone would take my place immediately. So, they shouldn't have an issue with letting me go.

Lastly, there is a third option (although I am not sure how viable this is). Edinburgh rejected me but they did say that there is a chance of getting in over clearing in august (If i get very good grades). So it would be a possibility to just leave firm and insurance as they are and go to Glasgow if I miss my offer and to Edinburgh if i get very good grades. But again I am not sure how easy it is to get into Edinburgh over clearing...

TLDR: is it best to switch now, wait and hope to miss my offer or try to switch after I get my grades (and got into UCL instead of Glasgow)

I am really not sure what to do and kind of panicking because I constantly find myself just hoping that I will miss my firm offer...
Thanks if you've read through all that whining and any advice would be appreciated!