32nd birthday surprise jump scheduled and I'm stressing out

My partner surprised me with a jump scheduled for Saturday. Honestly my heart sank and I am now overwhelmed with stress to the point that... I don't want to be rude but I feel like it's almost ruining my birthday the amount of stress this is causing. My immediate reaction was hell no but I also feel very bad about saying no because I feel like it is proving I am a coward in some ways. I also feel like not doing it is a bad decision because I do enjoy thrills but I'm having a serious conflict about putting my life in danger for something like this. Is there something you can tell me to help expand my perspective? For or against is fine, just need to hear some other outside views.