Are the fluctuations like spikes? Then more filter capacitor will help. Either across the supply rails, or from output to a supply rail.
Or else this problem may require a more stable voltage at the bias (meaning less resistance to your stable V reference),
or greater current capability from the supply,
or that you substitute a device that has less internal resistance at the output.
or that you add a buffer (voltage follower) after the output.
or that you increase resistance of your load connected to the output,.
Etc.