My date dumped me the night before homecoming, what should i think?

I know its alot of details, but i feel that its important that i understand why she was so upsett... Ok so i have a very good friend that i trust with my life who comes to me and says this girl who is her best that i know really wants me to ask her to be my homecoming date. Now im nothing excepttional especialy now cuz im on and off crutches due to ACL reconstruction n a meniscus repair (3 weeks ago) she seemed very fine with that and almost seemed glad id be a little more cautious while dancing. So, i ask her and she says yes, texts me ocasionaly (we talk a lot) and tells me shes so excited and cant wait. She also told me sge wants to be bf gf, i like her so i agree, so for two weeks we hang out a lot at school and hold hands and gradualy grow closer, no kissing or anything (she wanted to take things a little slow but was ok with holding hands n all) so i buy tickets and order a corsage. We plan out a whole group get together b4 the dance and she seemed thrilled, so we go to the football game the night b4 the dance and snuggle under a blanket cuz its cold (also a mutual thing) and shes all smiles. My bro calls and says we need to leave, so i crutch my way up to the car, then go back to offer her a ride. When i get back shes crying and surrounded by other friends, i sit down and gently adk whats wrong and she tells me shes really sorry but she just cant date me... I say its ok i understand, inside im crushed but i give her parting a hug and go. So she still uses the ticket n goes with other friends, i call to late to cancel the corsage so i pay for it, but thats only money its replaceable, now im wondering what i should be thinking... The entire time we were "dating" her best friend whom is aslo a close friend of mine tells me shes happy and were doing good... And then that happens... So was it something i did?