I had my heart set on Dentistry at Kings, but was rejected after interview. I was offered a place at Belfast and, although I wasn't too keen, put it down as my firm as it was the course that I wanted to study.
I had too many other commitments and jobs etc. during my a-levels and ended up with much lower grades than expected. I didn't get into Belfast, but got a place at Plymouth for Biomedical Sciences (without looking at the uni rankings :/ ). I decided not to retake a year and will hopefully study Dentistry after my degree. Think about all the stress you went through etc. during sixth form. Uni will be much more relaxed and fun, and, at the end of the day, you'll be on the right track to getting a degree in the subject you want. Who cares about which uni, or where - wherever you go, you'll make friends, have good tutors and a good life if you put in the effort.
I'd say retaking may not be worth the time, effort or risk of not improving.
Woahh, I didn't mean to make my post that long, sorry for boring you, but anyway, you now have
my opinion!
Alice