First of all I'm sorry you have to feel so anxious about your A Level results, this is a critical time in your life and you shouldn't be worrying about having a roof over your head too. Oxford is very ambitious and I commend you for that. If you don't get it, do you have other uni options? And rather if you don't get Oxford, but another reputable uni course that would lead to a positive career? If so I wouldn't be too anxious, and I'd doubt (but can't quite gather), your parents would kick you out if you didn't get Oxford but got UCL let's say.
I'll be frank as well, from my experience most employers don't care what uni it is. If it's a top 100 uni and you got a 2:1 lets say, great! That won't crumble career prospects exactly, it's just prestige and it can be a little futile, but good still to be ambitious and seek wisdom.