IF the water level is not rising anymore, turn off the water and let things sit, overnight would be good, but it probably won't take that long. Check the water level in the tank. You'll probably find that the water level has dropped, indicating that the flapper valve needs replacement. Some water can leak out of the valve some while it is open...that's normal. If the level isn't rising and going down the overflow, it sounds like that portion of the problem has been solved.
One visual symptom is if the flats around the edge are cup shaped verses horizontal..if so, the rubber has gotten soft and the flapper needs to be replaced. If it looks good, lift it, rub your finger around the seat to see if there's any crud and it's smooth.