yoga opens door to evil? IDK WHERE THIS GOES

Today I started my junior year of high school, and when I got home from school I asked my mom to sign her portion of class contracts.  When she got to my gym contract, she saw that I was taking yoga and demanded to know why I was taking it.  I informed her that the other gym classes-- basketball, soccer, volleyball, weight training, and different kinds of dance simply don't interest me.  (I did do martial arts second semester of my sophomore year, and I didn't mind it.)  She told me that when you do yoga, you don't know whom you're mediating to and could open doors to the devil. I told her I don't believe in that stuff so why does it matter? For me, it's not even about meditating, simply stretching.