Personally I would advise you stop this unauthorised moonlighting.

If caught, serious enough given the sack. If you lucky maybe get away with a serious warning letter for this infraction. but then your prospect for the rest of your career there will be affected.

There have been many cases people thought under the table money no CPF, bank transfers safe but in the end still kena caught. If your part time comes with CPF is not whether get caught, is when get caught.