Most of what I say will be more down to my own failings.
I've got a hunch that for Cambridge in particular, your interview is what essentially makes or breaks your application. I know people with average grades who've made it in and then people with insane grades who were rejected! In my feedback, there was nothing about my grades (which aren't particularly spectular) It was all about my interview. I think the gist of my feedback was that I was good, but there were just people who were better.
Also, I wouldn't worry about having 90% across your AS subjects, this seems to only be really vital for Economics and the sciences. Even the odd B at AS, isn't neccessarily much of an issue if it is in a unrelated subject. Getting strong UMS *(93%) in your top 3 subjects means that you won't be rejected outright, and will be automatically pooled regardless of your interview, so this is a plus for strong AS results, but can sometimes just prolog the pain.
I also do think that some colleges are 'slightly' easier to get into regardless of what people say. Obviously, you're best of choosing the college, which is best suited to you, but its good to consider some under-subscribed colleges for your courses. For example, I know a handful of people who got into Homerton, who themselves felt that they may not have got in hand they applied to a more competitive college. Apply to a college you like, but if you apply to a crazily competitive college, you may be pooled to a college which doesn't suit you.
Even though people say that you can't prepare for your interview, its still really important to ensure that you're really well-prepared. I stupidly bought into the idea that 'you can't prepare for the interview and basically was caught cold in the interview.
Make sure that your other choices are 'almost' as good as Cambridge. I know too many people whose second choice was somewhere like Sussex (no disrespect) and ended up feeling like they've sold themselves short. Nowhere can really match up to Cambridge or Oxford, but if prestige is important to you, try and have a few top 10 universities in your five choices to prevent the fall hurting as much!
Also try not to let it consume your life
Sorry about the essay!