It will probably be fine. However, the stuff you poured back in has had some of the solvents evaporate away and as you continue to do this the can will be become slightly thicker. I usually pour my excess into a seperate container (jelly jar works well) I then will use this first and supplement from the can. If the stuff in the jar is thick or lumpy when I go to use it I will either chuck it or use it in a less aesthetically important spot.

: I just applied the first coat of Flagship varnish to my hull. I carefully
: poured about 10 oz. of varnish from the new can through a strainer into a
: clean plastic container and used a foam brush. Everything went fine. After
: finishing, I had about 5 or 6 oz. left in the container. My first instinct
: was to discard it, but at 28.95 per quart I couldn't bring myself to do it
: - back in the can it went. Did I just doom the finish on my boat for the
: sake of 5 bucks worth of varnish?

: Jim