I'm not sure how VCE links to atar exactly but 55 is perfectly achievable for anyone willing to put in effort. kind of depends on a few factors eg personal ability, difficulty of your subjects but overall you need to put in a good amount of effort!
you can look at an atar calculator to see what marks you need in your subjects. not sure if you're in year 12 already but if so, there's still plenty of time to study and try your absolute best in your exams to get the score you want
you should definitely look up a few pathways into your preferred course though in case you don't get the atar you need, there are many options including tafe, doing a diploma before a bachelors, transferring into your course etc.