Legal Question in Criminal Law in California

Don't know if California has a law against it, but it is a violation of federal law. Yes, you should be worried.

Distributing controlled substances through the mail is a crime under both state and federal law. Since you don't know where the drugs are, it is quite plausible the authorities found them and are preparing a case against you.

Did you include a return address that can in any way be linked to you? If so, absolutely. Yes.

Duh. The only reason it didn't arrive is that it was intercepted by either postal workers for their own illegal use, or by law enforcement who would be preparing criminal charges against sender and recipient. Just how foolish is it to mail illegal contraband through a system that X-rays, drug sniffs, and otherwise inspects EVERY package???