I am planning to apply to St.Andrews, and my course requires AAB at a-level. I received ABBC at As-level, is there much chance of me getting an offer or applying?

yes there is a great chance

now stop whining and apply! it's only a single place on your UCAS form!

Tbh i cant stand it when people asks these types of questions...if you want to go somewhere, apply there...regardless of your grades....that's if you can spare the space on the ucas form. As long as you to at least 2 places which you are fairly confident you can get an offer from, you have np.