“You are [doing well]. You are just in the deep end of the pool- kind of like an academic Olympics, where everybody else is also a super strong swimmer and only swimming in their best event.”
And don’t underestimate how well prepared British students are, especially at private schools, for the first year of their Oxbridge courses. For example, whereas most schools would teach to a subset of questions on the A level math exam (IIRC you had to answer 8 out of a choice of 20+), we were prepared (mostly by teachers who had been to Oxbridge and had PhDs) for every single question, so it was relatively straightforward to get 100% or very close to that.
I was able to more or less coast through my first year and get a first because we had covered so much extra material at school. Only in the second year did things start to level out (I just missed a first that year), so I had to knuckle down and work hard for a first in finals when everyone was competing on equal terms.