There are two explanations for the wine being too sweet.
The first is that too much sugar was added at the beginning, so the wine reached its maximum alcohol percentage of 13-14% before the sugar was all used up. In order to test this accurately you would need to use a hydrometer.
A more likely explanation is that the fermentation didn't complete, which is usually caused by the wine being stored in temperature which is too cool. To make the wine drier you can adjust the brewing conditions and keep the wine in a warmer place.