To be honest, you need to have a stronger reason to get it remarked (not trying to hurt your feelings here. I can see you are disappointed with your result). In order to get a remark, your principal needs to do some paperwork, which means you need to persuade your teacher and your teacher then needs to ask your principal to fill in the form (such process will be tough).
Yup, and according to VCAA, the error in marking must be "objective" for scores to change. This means VCAA genuinely must have screwed up for this to happen. If you think an unfair mark has been given (eg. 4/8 instead of, say a 6/8) that is subjective and is very unlikely to change, especially for humanities subject where subjective opinion is required. Therefore, the standard to be met for remarking is really high.
Also, keep in mind remarking generally will be done by a very senior assessor (eg. Chief Assessor). They usually know the content better, and may likely be more harsh in their marking than other assessors. As said above, there is no reason why your score can't go down. That is a risk you must accept. All exams will have been marked by 2 or more assessors so the risk of mistakes is probably quite low.
All in all, the VCE system is quite fair and to be honest, what you experienced in marking was also faced by other students so I wouldn't go for a remarking unless you genuinely feel VCAA objectively made a mistake (Eg. wrong marks given, failure to award marks to an entire page etc.)