dont worry !!! =).... my 7 pound yorkie did the same thing.. he actually had about half of a one sheet whole cake.. of chocolate.. he was staying with his baby sitter and well the cake was left on the table it took one second for her to go up stairs and downstairs when she notice he was eating the cake....
i called my breeder asap and i told her what had happend.. i was crying.. and didnt know what to do.. but cakes dont have enough chocolate to kill your dog.. it might make him trow up and maybe have diarreah but he wont die... just be carefull with the chocolate bars.. that is a total diff. story!! =0) i hope ur baby is doing just fine...