Yes, to retake HSC. No to doing HSC next year.
If you are planning to do the same subjects for HSC, you have to redo that subject, even if you already know everything.
NESA states: You can repeat one or more courses within the 5 years without a penalty. Your RoSA will report the results of all attempts. If eligible, the Universities Admissions Centre (UAC) will calculate your ATAR from your most recent HSC results.