I had a similar issue on my latest build, when I tried using 3M's "Sharp Lines" blue tape to mask off the varnished gunwales before painting the deck.  Needless to say, it proved to me, again, the danger of using a new product without testing it first. Total disaster. The fix turned out to be relatively easy. Brush on some of the same thinner that you use for the paint onto the problem area and use a straight-edged plastic scraper to gradually remove the paint. It worked for me, even though a few weeks between disaster and removal had elapsed. 

Hi DMK, 

i would use a variation of Peter Shapiro's technique above.  some paint thinner of a white paper towel.  if the paint is relatively fresh, after a couple wipes, it should come off.

varnish can also be polished to bring a shine back if it is slightly flattened.  i have also touched up varnish in the past without redoing the whole surface with just a little bit of varnish wipe on with a little paper towel.   from a couple feet back, impossible to detect.

don't worry, this is a pretty common thing....and like i said, if its fresh paint, thinner will lift it quickly.

h

   Thanks for the info!  I was able to remove the paint with thinner and a green scrubby - it resisted any other method!  Lost a little of the varnish luster on one spot.  I'll try your suggestion of wiping on some varnish to fix that.