First of all remove all myths & misconceptions from your mind about masturbation
In fact, Masturbation is completely normal & doesn't have any bad effect to the body and mind.
Regarding the problem of acne, it can be due to various reasons like increased sebum production, blockage of the skin pores, inflammation, bacterial infection, etc.
Management involves application of Retinoids, Benzoyl peroxide
& taking antibiotics like Azithromycin
under the guidance of a Dermatologist.
So, it will be better to consult a Dermatologist
to find out the exact cause & start treatment accordingly.
Wishing you a Healthy Life.