(*Disclaimer: I am not a doctor or current med student. I am an applicant like you and this is my own personal opinion; I hope it helps)
Firstly, congratulations on your offers, you've obviously worked hard to get them and wouldn't have been offered places if they didn't see the potential in you.
Sometimes, we're our own worst critics, so believe in yourself, I'm sure you'll be great.
I have an honours degree in another science subject so I get why you would be worried about the information overload but from what I've heard about medicine, if you prepare and study often - in a way which works for you - you won't need to catch up as you'll be on track.
I've been told by family and friends that it's not overly difficult, it's just a lot of information. As mentioned above, once you master the studying routine that's right for you, you'll do it naturally. Some topics/areas you'll understand no problem and others, you'll maybe struggle with and require more support.
There's online flashcards to help with memory where you can write things down and test yourself (I believe it's called Anki).
Buying loads of books is most likely going to add to your stress and the university should provide you with what you need.
I have however, heard that the 'Zero to Finals' flashcards/book is pretty good if you're looking for something though but again, this isn't me talking from experience, just going on what I've read and heard.
If, for any reason you feel that you're falling behind, definitely seek out support from the university.
Best of luck with your exams and life at university. Be positive!! 🙂