remember that tart and sweet are not exactly opposites either, think sweet and sour sauce, it is sweet and it is sour so I would not recommend sweetening at all yet, especially if it is young. at two months you are just starting to see the character of the wine, which is not fully developed by any means, perhaps the tip of the iceberg.
if it is entirely clear and no lees, then I would say let it age a bit and see what happens in two more months (check sulfite levels).
did you test your PH or TA before fermentation? and did you taste any of the fruit?
if there are lees I would get it off the lees, and check your sulfite levels place under air lock and then wait two more months.
I didn't see any pectic enzyme in the recipe, maybe others can clear it up further but my first inclination is that there isn't enough fruit there in the recipe.
did you add camden tablets to the must before you added yeast, and how long was it before fermentation fully took off? are we sure the montrachet did the job or was it wild yeast....