There is a notion in lower education that so long as you try hard enough you can do anything. This is a lie we tell children, similar to Santa Claus.
At university you will judged against those who are naturally gifted, against a course that is meant to push them to their limits. Through time and effort you may be able to get through, but you will never be top of the class. The course assumes the student is both academically smart and is willing to put a lot of effort in. If you can only offer one of those you may struggle.
I would also point out that you've picked an unusually sadistic course. In a straight physics degree there are some modules which are so mathsy, so horridly brain destroying that only the most academically gifted will choose to take them. Those modules form the compulsory components of a theoretical physics degree. So while other students may have chance to boost their grade averages with 'easy' modules like programming, you will be forced to take general relativity or quantum field theory instead.
I appreciate this sounds cynical, but my academic experience is similar to what you plan to do (MPhys theory), and I've seen plenty of students put every waking moment in to their work, and still barely manage a passing grade. In four years of university I've seen three guys break down in tears for this reason. The bar is just so much higher.
EDIT: Dear OP, I glanced over your case history in your footer. I stand by what I said, but if there is one student in a thousand who manages to achieve through hard work alone, you deserve to be them. Best of luck.