After I worked it down and sanded it smooth, I applied a skim coat of resin to fill some tiny holes, and it isn't curing fully. Undoubtedly I was a few drops shy on the hardener. It's still slightly tacky, just enough that I can't sand it, even though it sat in the sun all day.

Any tips to get it to fully cure? I seem to remember that in the past I have mixed some more resin, super "hot" with hardener, and skimmed the part.