The 5% who do react get acute renal failure which is untreatable and often terminal within a very short space of time.
To those saying its a myth - this you may be happy to gamble your dogs life^ over relatively cheap preventative treatment but to advise it's a myth or not to bother taking to vets is incredibly dangerous.
There is no way to know if your dog is one that will react to just getting a tiny amount once, one that will only react after getting them occasionally over a long period of time or one that will be fine with loads over a prolonged period of exposure. They cannot work out why this happens, meaning there is no way of knowing if your dog is likely to be affected or not.
Sue the key in your situation was it was a couple of days later. It was too late for emetic or carbon - so nothing they could do, plus in all likelihood your dog would have already started to go into renal failure if they were going to react.
Op you acted quickly, so hopefully everything will be ok. I've got a little dog (Cavalier) who can jump onto the worktop. Thankfully for me, it was only some offcuts from a pork joint that my dog stole, so no harm done and I learnt not to leave food on worktop, and make sure dog can't access kitchen without me to be doubly sure. It's something you don't expect from a dog less than 1ft tall! So don't blame yourself. 