Seriously, talk to the admissions office at Cal. Explain that your Spanish grade is dropping because you've been ill.
When an admitted student's grades drop, the first thing that happens is that the student gets a letter from the admissions office asking the student to explain why. If you have been ill, you can explain why. They want to work with you. They wanted you to go to Cal, and they still want you to. They don't want to rescind their offer of admission.
(NOTE: this advice is, of course, predicated on the assumption that you've been legitimately ill, and that you're not just slacking.)