Im really sorry for you mousy, like theduffy said, i don't really know you but i really feel for you. But look on the bright side, you will have a lot of fun at st andrews, probably more so than at cambridge coz it won't be so tough all the time. And if you're of a high enough standard to get pooled by cambridge (bearing in mind i know some real super-genius ppl who got rejected) then you will do well wherever you go.
Anyways good luck!