Squishy you're lucky that you have an offer! Think of those who don't have any offers(like me!
I would advise you to seriously consider it before you make any impulsive decisions... there is no such thing as better/top medical schools after all, they are medical schools! You're applying for medical schools, not for the universities!
After all, no one is gonna care about what medical school you go to once you graduate, you're a junior doctor and how skilled you're depends on what you've gained in the 5yrs.
If you really really really hate that school, then reapply, but be mentally prepared to get no offers at all(I know this might sound harsh) as the competition for medical school is increasing every year. Just look at the bloody average ukcat score!