Help What Do I Do My Friend Will Be Mad?

I told my friend a couple weeks ago I was FOR SURE going snowboarding this year. We were planning on going together. But then I decided a couple days ago (and didn't tell her yet) that I really don't want to anymore after realizing there are a lot of cons for me. Meanwhile my friend just texted me saying she got new snowboard pants and asked me again if I'm for sure going snowboarding..what do I say?!?! She's gonna be mad, and she's the only real friend I have left due to my past stupidity...