Roy Boy: Re Fermenting on Skins with White Wine.
How Long have you had the wine on the skins?
How warm is the must (Ie are you keeping it cool).
What Varietals are you fermenting?

I have made white wine from grapes for the past few years
with a cold soak in a fridge at 50F/10C for up to 4 days +
a Short warm (20C) fermentation of 12 hours or or less Plus a
cool fermentation (15C -60 F) or less for up to 4 days ON SKINS
before bladder (gental) pressing off the skins. The Fermantaton
continued of the juice/wine for another 6 to 18 days at cool 15C/60F
or less temp. This results in wine with much more varietal
characteristics
and more bouquet and body.

If you keep the Must cool and have not gone beyond 4 days on the
skin you should be OK .
If not sure or unwilling to risk it ,press as soon as possible .
Continue
to ferment with as little air space and cool tempertatures as possible
until fermented out to dry nes or where you want the residual
sweetness.
I hope this helps