UK A levels in UCLA admissions contract

Hi all,

I study in the UK A level system and I was wondering to what extent the stipulations in the UCLA admissions contract are strict? They have said that I must get at least all B grades and that I must not fall significantly below my predicted grades (A*AAB).

Is it true that they would rescind my offer of admission if I were to get say, AABB? Would they actually do this? Given my predictions above, how low a level would they accept my A level grades?

Thank you!