With tapes the evidence you will see is little pieces of the host worm which is still in the cat. The segments look like pieces of rice.
As the medicine is determined by the weight of the cat, and the cat didn't get much medicine, or vomited most of it up, you may not see dramatic results. It depends on how much the cat actually kept in the system. If you see the grains on the back legs and the rear and they aren't moving, that's a good sign.
The good news is that tapeworms do not do major damage like some other parasites do. But they do rob the cat of nutrition and therefore the cat will be hungrier than usual. They need to be taken care of, but first talk to your vet and find out how best to proceed. This is not a life-threatening situation, as long as you talk to your vet, tell him what happened and he will advise you from there.