Sounds like it'd be best to make the bike work for you..unless you just have buyers remorse and are looking for reasons to get out of this purchase. Not trying to be insulting; it just seems like there's a lot you can do to make the bike what you want instead of taking the colossal financial hit of selling it. No one gives a crap what cassette you have. Short of putting MTB handlebars on it, no one cares. a 12-28 cassette makes a lot of difference for cheap money. A friend has a 32 and it looks like a freakin' dinner plate compared to my 28. Good luck.