Just go to the website and look at the requirements and don't listen to most "TSR" rumors. There is a test for Top UK universities in medicine called the BMAT, this will likely play a large factor for Cambridge application to get you at least to the interview stage. Your GCSEs are fine, hopefully they are above the average in your school.
try to get predicted A* across the board
Do well in the BMAT
Try to score High UMS in AS exams
Also i have to stress you need to do some extra reading outside school and really love medicine, there are a ton of great candidates with the same grades as you if not better, you need to stand out by doing stuff outside school like wider reading, volunteer work, shadow a doctor etc...
If all goes well you should be able to get to the interview stage which is amazing in itself. After that it's all about keeping calm, knowing why you want to do medicine clearly, and being able to have a strong deep discussion about medicine but also have alevel concepts clear in subjects like biology and chemistry