Should I do the superday for BB after accepting an offer at another firm?

here's tldr:

• I got invited to superday for S&T 2020 internship at Credit Suisse, taking place next week
• I already accepted offer at a lesser tier firm in S&T, great company abroad but not so much presence in US. I have connections at the firm, including MD in diff division who first introduced me to the firm last year. I've chatted with other current analysts and accepted.
• After accepting within their 5 day deadline (which should be illegal), I had rejected other invites to interview, including another superday.
• I want to attend the CS superday, thought maybe if I go to CS, I coud land a full time position in a BB, rather than try to move up from the other firm. Of course, no guarantees, and don't know the return rate for CS, but at the current firm I do have a better chance since it is "less competitive". I don't want to burn bridges - I feel guilty but also don't want to feel regret.
• The problem is I cannot attend the superday! I have midterms next week, and one happens to be then. Already emailed about time conflict.

Should I reemail saying I withdraw from the process?