I'd be worried if I did put my heart and soul in to the HSC. The HSC is ultimately just a fairly questionable representation of your ability to work hard in subjects that largely don't interest you. Why should you put your heart in to such a superficial goal? Uh, you shouldn't. Sure, it's important, and so there's something to be said for putting a lot of effort in...but again, why should you?
It's not life or death. When you're 40, or even 20 probably, it will mean nothing. It's not a definition of your life. These are all obvious and cliched points but they're true nonetheless. Life's about fun, especially at our age, and finding satisfaction. And you'd be hard pressed to find true satisfaction from studying for the HSC.
I'm sure everyone is capable of doing well, regardless of your 'natural intellectual ability' (whatever that means). I'm sure I could've gotten a UAI of 99 if I was motivated, but instead I chose to put my 'heart and soul' in to learning about the history of Australian independent music, learning guitar and piano and bass, recording songs, relaxing in cafes and bars, going to parties and having a good time. And I reckon my 'heart and soul' is a lot more fulfilled than someone who's going to get a higher UAI than me but had a boring and overly stressful year. But then, that person with 99 probably disagrees.
Anyway, rock on and have a good 4 months break!
Anton