Going to COB events isn't a pain in the ass like formal rush can be. You basically go to a party and hang out with a lot of nice girls and probably do something fun - the time restrictions and things like that aren't present. It's much more relaxed. So I would definitely look into it - even if you don't receive a bid you most likely will meet lots of nice people and have fun.
Also I would double check with the registrar and the Greek Life office to make sure everything is squared away with your GPA transferring. This may have been one of the reasons you didn't get asked back anywhere during formal rush.