Spar varnish is a odd beast it also never gets really hard it is designed to flex (spar like a boat mast) they as Vypyrz stated take a long time to fully cure. Heat and air is the only way and at that is will take a while, when I was younger I built boat for a living and we used a drying shed that was in the mid 80's with barn vents on the ends it would take a week before it was hard enough to move. Exactly what varnish did you use? (for your sake I hope it wasn't deks olje great stuff on a boat but it out gasses for years)