I believe (could be wrong, but I think I read this somewhere), that with UCs, you can only submit the SIR to one UC. Therefore, you are obligated to enroll at the first school you submitted it to (in this case, Cal). This probably explains why you were unable to pay for the UCSD SIR; you are logged into the UC system database as a Cal student.
Honestly, everything happens for a reason. I'm sure Cal was well thought-out and you'll love it there. Be happy, it's a great school
