OP, hydrometer samples will be your best friend in wine making. In particularly if you are not working from a pre assembled kit wine. Generally the advice for a finished wine would be to blend the wine as everyone has already said. Some things to keep in mind in the future is that generally adding additional sugar to the wine pre fermentation will increase alcohol content which in turn lowers perceived sweetness. However, and I feel this is what happened in your case, you can add too much which will cause your starting gravity to be outside of the optimum range of the yeast which will cause the yeast to stress and not finish the job - leaving behind unfermented sugars and the sweet taste. By taking a hyrdrometer reading before adding sugar and knowing the optimums of your yeast, you will be able to determine how much sugar you can add and determine pitching rate for the yeast.
Good luck!