Absolutely, first of all you wanna talk to your subject teachers about your goal, and hopefully they'll give you resources like mock exams etc you can do yourself in timed conditions etc or essays even, give them in and have your teachers assess your work. Also ask to resit mocks and just keep doing extra work if you wanna be predicted higher for you unis and if you wanna get good grades overall! don't push yourself too much though, but you can do it if you really want to and strive for it!
Goodluck!!! (: