do i have to pay anything back?
No. Scholarships are 'gifts' of money, not loans, and generally there is no requirement to pay anything back.
However, if you do not satisfy the conditions of an award, you may be required to return scholarship funds.
Some scholarship rules stipulate that you achieve certain grades, such as a 'Credit' in all subjects, in order to receive further instalments.
Or you may be required to attend an awards ceremony or report back to the funding body on your educational progress. You should look carefully at the terms, conditions or rules and find any other information about the scholarship provided by the university or independent scholarship provider.
If no details are given, enquire before you apply. Finally, it's important that you "do your homework" around how a scholarship may impact upon any other payments you might be receiving.
It is important to understand that some government payments, such as ABSTUDY, can be affected by scholarship payments. For more information see how much does university study cost?.