Your a levels grades will be more important, but GCSE grades do matter for medicine. I would still go for it, but just make sure predicted grades, ps, and scores on BMAT AND UCAT are as strong as possible. Do you not want to do med at a ‘bad’ uni because of its ranking, or because you feel like the course will not be as good as one from say imperial or cambridge? Because if it’s the latter, then it doesn’t matter which uni you get your degree from, as medical school is hard to get into in general, and all courses have been designed and approved to set you up for the field, so there aren’t really ‘bad’ unis for medicine.