You have a couple of options, don't worry and revise the best you can for the BMAT,
lets say you for some reason don't get the results you want, do not give up here
focus on your A- Levels and get the grades, this will give the option of a gap year and reapplying with more time to focus on the BMAT and UKCAT,
and don't let the ukcat dishearten you, it different for everyone, you might have been unlucky and got a set of harder questions.
Everyone takes the same BMAT, so if it is hard, everyone will find it hard