I really wouldn't worry about feeling out of place. Oxbridge admissions tutors make a living out of picking the right people for their course and as such they're undoubtedly very good at picking people that they know will do well. As a result their word holds some weight around college and thus, regardless of your grades, people will consider you good enough to be there because the tutors say you are. It's very, very rare that they make mistakes. I had similar qualms to you when the conversation turned to grades among the cohort of lawyers at my college - I only just scraped my A*AA offer while one of the girls had got 6 A*s. But then for the first year we both got 2:1s. And to be honest, anyone that looks down on you because of your grades isn't worth your time anyway, and will probably come off worse in life - whatever job they end up in they'll almost certainly have to deal with people who are less clever than them and that's not going to end well if they keep looking down their nose all the time!