What do I do to tell her I don't want to go-without letting her down?

My best friend is having her 15 birthday and she wants to take me with her. But the thing is.. is that I hate rides, I don't like disneyland and I really don't want to be stuck in a car with her and her family for 20 hours. But she's already decided (for me) that I'm going and soon she's going to talk to my parents about it. I've already told her that I don't like disney land OR rides but she won't budge. I don't want her dad to waste money on me for something I won't even enjoy. How do I break it to her that I don't want to go without letting her down?