Small changes in seat position can make a big difference. If your seat is not glued in, try moving it back an inch or so. You are at the light end of the weight range for this boat. You might try sticking a gallon jug of water in the rear compartment to see if that makes a difference. -Wes

You could also try a temporary skeg to see if that will do the trick.  I’ve seen a version that has a cone the slides over the back end of the kayak with a fin sticking out the bottom.  Thinking you could make a rough version of that or even just a plate with a fin (easy to make our of some scrap) and duct tape it on as a test before investing the time and effort into a serious mode.

I had the same thing with my SOF so looked into a removable skid using a fixed track and sliding the fin on and off.  I settled for a small permanent skeg that is serving the purpose, just shaped a bit of scrap cedar and two screws.

Hope this helps.

Thanks for the suggestion Wes.  I have not glued my seat in yet, so I will try adjusting it back an inch or so before my next paddle.  Also, I have read a little about balasting and tracking.  The author felt his boats tracked much better when they were loaded for an excursion.  

I still flinch at the word "weathercocking."  Back in the 1990s mention of the word on a bulletin board used to be followed by great fits of passion and distemper from various paddling community factions, lasting weeks or sometimes years.  One clique could be relied on to insist that any need for a tracking aid was proof of incompetence and perfidy on the part of the kayak designer.    

Passions have cooled, fortunately.  The problem is that as you dial out weathercocking on the drawing board, various other even less desirable traits emerge.  The formula is complex but the simplest way to erase weathercocking is to reduce hull rocker (how much the boat rocks from bow to stern when placed on the ground).  This leads to a kayak with twitchy, unpredictable behavior in waves.  Adding rocker can convert a kayak that's cranky and awkward in waves into a fast, nimble surfing machine.  And that describes the Night Heron perfectly.  

Payload, the shape of the bow and stern, and the skill of the paddler all affect tracking just as much as keel rocker.  Loading the boat by the stern might help a little but it's kind of like putting cinder blocks in the trunk of a BMW E30 for better grip.  

Want the best of both worlds?  A retractable skeg.  There when you need it, stowed when you don't.