Honestly there is nothing wrong with not knowing what you want to do at uni, lots of people quit before the census day or change courses so you're not alone! Just go through the course handbook and find out more about what interests you. Talk to your careers advisor as well. Remember the cut off for changes through uac is well after you find out your atar - and you can always defer if you're not sure. For motivation to study - just think that the better the result you get the more options that will be open to you! The great thing about not having chosen a path is that the sky is the limit!