If i dont do well in year 12 and get a good enter score will i not be able to get where i want to in life?

So basically Im in year 12 and im getting all stressed out cause i dont know what to do. Basically im doing psychology, IT, Drama, Media and english language, Im not the best student, and i get marks around C+ standard, but i know that if i put my mind to it, i can actually do really well, Im just not really much of an academic person, ive been told by respectable directors and actors that i have a talent with acting, and that is what i wish to do later in life, im also very good creatively, i play drums, and i create music with audio interfaces on computers, however im not good when it comes to drawing. My parents are very intelligent, specifically my dad, my mum is better at english rather than scientific topics. Anyway, basically im not doing the best I can be doing this year and I just really dont want to be some drug addict on the side of the road with no job, I will never ever EVER touch any drugs other than a little bit of dope here and there, ANYWAY, i also want to know, Is it really worth being one of those kids that put 3 hours of study and homework in every night? Because at the moment im lucky if i do 30 minutes of study/homework, im getting by OKAY with that, but i know i can be doing better, is it worth myself doing that? do i need that realisation to get off ******* WoW and start putting the work in. I have my mid year psychology exam tomorrow which i have barely studied for and im hoping to 'wing' it, so if you suggest i pull my finger out of my *** and do those 3 hours or whatever a night and be a good child like that then ill have to start after my mid year exam tomorrow! please help me out, im not one to ask for help normally but i feel i really need to!!