fiberglass strip??? I believe the strips are wood, leastways they were wood on my Kaholo SUP. 

Get a good hair dryer and heat the strip/ply joint and start prying - hot epoxy will give it up and strip should be removable. Sand off excess epoxy, glue strip back on correct side. continue . . .

Yes fiberglass cloth strip.  The directions dictate cutting a 3inch strip, covering the inside of the  puzzle joint.  I glued last night has to much time passed to heat and try to remove fiberglass cloth?

Forget it.  I did the same thing.  use it to support the joint, assemble the hull, then sand it smooth.  I will disappear under the cloth when you glass the hull.

I've done that!  Several times.  No big deal.  The fiberglass turns clear during the finishing process.  Just sand it smooth and it will vanish in later steps.  

so I was really impatient last night and went at it with my heat gun on low heat setting.  The fiberglass strip peeled right up!

Now I'm left with messy epoxy.  Should I wait a few day for a hard cure then sand down to a wood?

Try a scraper... scrape first, sand later.

Keith

My error - I built from plans and scarfed the ply rather than join via a CLC puzzle joint so you fiberglass strip thing had me confused. As you discopvered, heat works. Soon as epoxy cools down you should be able top scrape it off.

The beauty of wood boat building = even if you pull a major screw up saws, files, grinders, scrapers, and sandpaper can fix it.