That sounds like a good plan to me. Have you also tried denatured alcohol? If that also works to remove some of what you can't scrape off, its vapors aren't as obnoxious, and it could save you from gumming up a lot of sandpaper. It wouldn't cause any harm to try, if you have some on hand.

Old Yeller

I had a similar problem when I failed to adequately mix a batch. Skip the sandpaper for now - you'll just be wasting it. I used white vinegar and furniture scrapers, which got almost all of it off without disturbing the cured epoxy underneath. Then finish up with 120-grit paper and reapply fresh epoxy.

I second the vinegar.  Been there, swore at that.  

The vinegar loosened things up enough to remove the "oops" and get down to the properly cured layer without damaging much.  It's lucky that Costco has the stuff in multiple gallon packs...

It took a while and I would work at it for a while, then let things dry (or, at least let the vinegar react and evaporate for an evening).  It took three or four evenings of apply, scrape/towel, and let dry before I was down to what seemed to be pretty solid epoxy.  Dunno if I actually needed to let things dry or not, but it worked for me.

Vinegar also works wonders when your hands are covered in epoxy because your gloves ripped. by the way.  Not that I've ever been so careless...

Vinegar also gets it out of your hair when you've leaned into the rear hatch of a WD, gotten the gypsy scarf caught on something to where it pulled off and put your hair into uncured epoxy trying to tape the deck to to the hull. Beards, too. Purely theoretical knowledge - nudge, nudge, wink, wink, say no more.

Laszlo

Vinegar is fine for removing uncured epoxy from tools and such (while wearing gloves), but isn't the best thing for epoxy on skin. It probably falls into the category of solvents that actually cause the epoxy to be absorbed more completely, and I've read advice from a few professional builders not to use if for that. I would also be careful to thoroughly wash off any residue after applying it to a boat.

Here is West System Epoxies' advice: "If you do get resin, hardener or mixed epoxy on your skin, remove it as soon as possible. Resin is not water-soluble, use a waterless skin cleanser to remove resin or mixed epoxy from your skin. Hardener is water soluble, wash with soap and warm water to remove hardener or sanding dust from your skin. Always wash thoroughly with soap and warm water after using epoxy, removing amine blush or sanding epoxy. If you spill epoxy on your clothes, change them immediately. Use skin cleanser to remove any epoxy from you and your clothes. If you cannot completely remove it from your clothes, do not continue to wear them. If it is mixed epoxy, you may wear the clothes again once the epoxy has completely cured. Never use solvents to remove epoxy from your skin."

Old Yeller

Smells like oranges - best hand cleaner going is citrus based. East to find, any auto parts store . . .

Vinegar to remove uncued epoxy from tools is the way to go, BUT if the tool is ferrous metal clean the tool after the vinegar clean with water, alcohol, minerl spirits, whatever or the tool will RUST overnight.

I've started using something called Bio-Solv, a soybean-based acetone susbstitute. It does a great job on tools, even with hardened epoxy. I would be reluctant to use it on skin, however, because it's still a penetrating solvent and I'd worry that it would carry what it was dissolving right through to my innards!  By the way, I recently made a mistake and used Bio-Solv instead of denatured alcohol to clean up the surface before putting in the final weave-filling coat of epoxy. I realized it right away from the foul smell and wiped it down with water and then alcohol and then more water and then alcohol again. No apparent harm, but it sure made me nervous!