Firstly, your acne is around the areas covered by the face mask e.g. mouth, jaw, cheek or chin area? If it is, then most likely it's due to the face mask. There a variety of possible factors e.g. you're wearing it too long or the fabric isn't suitable for you or the mask made you irritate your skin more etc.

If you wanna avoid facial places that lures you in with cheap 1st time session but pester you to hell with their expensive packages later on, then time to learn up some basic skincare. Understand your skin condition & get a good cleanser, toner (if you like) & moisturizer (hopefully with anti-acne properties).