The majority of medicine is not intellectually difficult. What makes medicine hard is the sheer amount that you have to know, and hard work and dedication will help you much more than intelligence when it comes to that. In some ways I think supposedly less clever people can have an edge in medicine, because they have learnt to work hard and develop good habits (rather than people like me who breezed through A levels and was a hot mess in med school)
Don't worry about being good enough for medicine. Worry about getting your grades. If you get the grades, you are good enough, that's why the requirements are what they are