Okay. I kind of do not want to post this, but I will. I do not want to hurt anyone, I am honestly trying to help.
I post this, because I wonder sometimes if I am feeling like you seem to be, and it worries me...about myself. (I am trying hard to properly express myself in that sentence)
Have you lived independently in the US before? In particular, in a large city? I will not be working (I will have financial support from my parents and loans), but I am 21, and I have already begun my Independence lessons - I have bills (one due today infact...), and I have been my mother's caretaker for some time, so I have had to take care of myself, and be alone for long periods of time in the past, since I was way too young to do it.
I am wondering, if you are set on the UK, if maybe a smaller (but still very cosmopolitan) town would suit you - maybe like Glasgow, or Brighton where it is a bit more affordable?
I have worked retail here in the US at a bridal shop as a summer job, in a large city with a very good cost of living, and trust me, that money goes no where! And I had commission! Oh, I was so glad I quit. I just don't want you to be miserable.
By January, maybe you'll have tons of pence saved up, and you'll be way more ready than I could be. Good luck!