Often uni's give lower offers if you are doing subjects that are relevant to the course you want to study.
Also, if you talk to a teacher of a subject which you think you will get a higher grade they have predicted and you are willing to maybe do a resit of an AS exam or to go to extra revision classes they may raise your predicted grade to an A.
They may also be other ways to get into the course, such as a diploma or a Btec?