Not sure if you should do this but what hell would break loose if you said "Thanks for agreeing to study with me Bob, but I don't want a bible study. It's my aunt who wants me to have a bible study, but I don't. I'm only here to please her and I don't believe Jehovah's Witnesses have ever predicted anything of significance that has come true."
"Furthermore, I do not want to waste my school years swotting to join a cult and so won't make any effort to do so."