Did I accidentally send my bank transfer receipt to the wrong email address?

Yeah, just to clarify, OP seemed to be sending the receipt to another person, not the bank. So, it really depends on how the recipient's email service is set up.

You're in the clear! Email addresses aren't case sensitive, so it should get to the same person regardless of that letter's case.

There's no way for us to know for sure, as it depends on the recipient's email system. If you don’t get a bounce-back message, it means the email was either successfully delivered or dropped. It doesn’t guarantee it reached the right person, though.