It depends on what is stated in your employment agreement.
If your employment agreement states that the percentage of gross billings is “50% inclusive of superannuation” then, as the superannuation rate is currently 10.0%, your salary is actually 45.45% of billings with 4.55% billings paid into your superannuation fund. (This is slightly above the NTCER minimum, which is 44.79% billings as salary and 4.48% billings is the super contribution.)
However, if your agreement states that the percentage of gross billings is “50% plus superannuation” or “50% exclusive of superannuation”, then the superannuation contribution should not be deducted from your 50% billings rather 5.0% (i.e. 10.0% of 50%) of your total billings is paid into your superannuation fund on top of the 50% of your billings which forms your salary.