Medicine is a competitive course in general, but if you want to apply to Oxford you have to have strong academics as well as extra/supercurriculars as they really do want someone who is very well rounded. If you still haven't done your GCSEs I would suggest that you try to get as many 8s and 9s possible and also maybe start doing some volunteering or something similar, this is for writing your personal statement, and I personally found it quite enjoyable. And when it comes to year 12, you need to ensure you do well in your mocks and in your UCAT as these are also a major part of whether Oxford will even look at you application, so basically try your hardest but do not stress out too much as you still have a long time to go!!
I applied to med schools this year, including Oxford, got rejected from Oxford but got all my other offers. Just remember not to lose hope, because wherever you go to study medicine, you will learn the same content everywhere and will end up being just as good as a doctor as someone who went to a different med school. Hope that kinda answered your questions?