The peach nectar will ferment out, and that means restarting fermentation. Of course, then it needs to be racked off of the new lees that form so the wine can clear. And when it's racked, it needs to be topped off.............
What I usually do is one of two things. Either I build topping off into the recipe, and make a bit more wine and keep it in a wine bottle/growler/one gallon jug/etc for topping up, or I top up with a similar wine. Since you don't already have peach wine to use to top up with I assume, a cheap white wine would work great.
If it's too much headspace to top up with without changing the flavor, the wine should be racked to a smaller container.