I accidentally marked a book received and I didn't get it. I got about 10 books in the mail while on vacation and marked one received which wasn't. Is there anyway to remedy this? I already sent a note to the sender outlining my mistake. Am I SOL if it doesn't arrive?

There is no way to undo it. If the book doesn't arrive the only recourse would be to see if the sender would give the credit back.

Unfortunately yes. Once it is marked as received (and trust me, we have all done it at least once!) you just have to hope that it shows up -- and nine times out of ten it will. So fingers crossed!

I did this not too long ago, with a book that was long overdue and coming from a certain state.  I got a book from that state and stupidly assumed it was that book, so I marked it as received even as I was opening it.  It was a different request entirely that I had forgotten about.    I PM'd the sender of the MIA book, telling her I marked it received in error, asked if she would please return my credit until it did actually arrive, and also asked her to confirm when she did mail it, as it was due to go missing within a week.    I contacted PBS and told them of my mistake as well.  I heard nothing from the other member and sent a second PM several days after I noticed the first had been read.  Still no response.  About 10 days or so later I got a response from PBS, and my credit was returned by them, I think mostly b/c the other member did not respond to my PMs.  I did get a gentle reminder to be more careful in future when marking books as received.  FWIW, I never got the book, and I would bet my car that it was never mailed to start with.