Today, Sunday I go stuck in the carpool only over p by accident. Am I gonna get a fine? How much?

Coming off the Bay Bridge, in Oakland, I went the wrong direction at the split so I got off 80 and went back on in the other direction but, this took me back to the Bridge (N-W)to S.F. without a choice. I thought I was taking the last exit only to find myself on a carpool overp getting on the Bridge which I did not want to do. Am I at fault and do I have to pay a fine? Are there any exceptions?