Already Accepted a MM Offer, Upcoming Superday at BB

Hi All,

I recently accepted a SA position at a MM bank in the DCM group in a non major city (think philly, baltimore, etc.). The day after the cut off for the acceptance date I got an email inviting me to a Superday for a FICC group S&T internship at a BB in NY. I really wanted to do S&T over IB/DCM but nothing worked out in time so I accepted the offer that I had. Should I still go to the superday? And if I get the offer how badly am I screwing myself going back to the MM and saying I am going back on my acceptance. I networked really hard at the MM to get that offer and don't want them to hate me for going back on my acceptance. Is it worth going to the superday at the BB or I am wasting their time if I already accepted my other offer and would harm my career by revoking my acceptance? Need to decide quite soon.