Congratulations on winning the Hackathon! Did you participate in the December Finals in Palo Alto and this blogpost is just many months late, or have they started a new round competition? If it's the former, I believe we've met (I was on the UW team), if it's the latter, best of luck!
My experience at the Facebook Hackathon was very similar - I was the only Freshman to enter, our team had been cobbled together entirely by chance (2/4 were found by posting on reddit). We were some of the last to demo, and every one that preceded us seemed, at least to me, far more technically impressive. People had built real time games, written web-servers, designed Android apps to handle streaming video, but (almost) no one had a use-case. We essentially strung together API on top of API in some of the most hacky code I've ever written[1], and somehow it all came together in the end to a) work for the demo and b) seem like something people would actually use. Our idea for the final round was far more derivative and banal, and we lost because of it.