If this is not the ice wine style kit then it probably didn't come with an f-pac and it porbably didn't come with any sorbate either. This is probably off-dry - maybe 1% or 2% RS?? What does it say your SG should be at this stage? I'll bet if you throw a little simple syrup at it that will bring out some of the Riesling's flavors and aromas - plus remember it's still young and it has to age a few months. You will need to add sorbate if you're going to add anything to it with fermentable sugar in it.
The sorbate should have been bag #3 that came with the kit...if you've already done step 3, that's the step when you add the K-meta and sorbate, along with what ever clarifying agent they have included.
As far as flavoring it...I would wait until it's done clarifying, and then taste it. Depending on the kit, you may have another racking to "brilliantly shine" the wine. If that's the case you'll need to top it off again, then you can add whatever flavoring you like.
Personally I would just follow the instructions...unless one of the steps was really goofed up, the wine should be fine after a few months in the bottle.