If it won't take any more resin and just stays white, then yeah, looks like you get to sand it off. Might try pulling it off with pliers (catfish skinning pliers?), try scrapers, try a wire wheel in a drill, try anything and everything that sounds like it might work. Use caution when experimenting, of course; the idea is to save retro time, not add hours to the project.

I once got about halfway through glassing out a deck and had an emergency call me away, couldn't get back to it for 24 hours. The "wet edge" I left was well defined, and the next day I simply took up where I left off, and it worked out well except you could see where the break in the action had occurred. But lo and behold, the demarcation faded, then vanished altogether in a couple days. That was on my Cormorant, in '04, and I'm still paddling that sweetheart.

Good luck with yours, and let us know what happens....?

: Okay, I blew it.