How to get a constant voltage output from a dc to dc converter?
Your circuit is the bare minimum to produce a boost output voltage - there will always be ripple in this type of circuit and if you want lower ripple try making the output capacitor bigger. If you really want a more stable output than what can be gotten from a bigger output capacitor then your switching frequency of 10kHz would need to rise considerably - typically, modern chips do this and switch at many hundreds of kHz and even a couple of MHz.

Ultimately, if you need a clean and quiet supply to can add a linear voltage regulator after the booster.