How to get out of going to this thing with my friend?

my friend, rachel, wants me to go to this play with her. its supposedly some version of macbeth. however, although im her friend, shes really much more into the play stuff than i am. i cant stand plays. they aren't my thing. i went to one once with her before, and i was ready to kill myself through the whole thing. so, i really don't want to go this time. shes not even asking me to go. shes telling me im going. i would make up an excuse and say i have something to do already, but she already went up to my mother and asked if i was free, and my mom said yes. so, she knows im free, and i cant lie to her know. i really do like rachel as a friend. shes a nice girl, but i really don't want to go to this play with her. id just much rather be staying home and watching the orioles game. how do i get out of it now?