At the risk of writing something that you don't want to read, why not do it over? You did it once and don't like the result. So every time that you look at the bulkhead (i.e., every time you're on the boat), you'll hate it. Why not suck it up and do it right. You'll be a lot happier and that's what a boat's supposed to do for you.
While PolyShades is most definitely a compromise, all Minwax products should not be grouped with it. I use gallons of Minwax Wipe-on Poly and Helmsman Urethane and have never had an adhesion failure when using fresh product. Even old stuff is ok, but difficult to get a good flow. I use it on the furniture that I build and Victoria's
interior. Good stuff that's difficult mess up.