yes, sand the socket with 80 grit. However, I'm not a big fan of adding catalyst after mixing in the filler - I get worried that you won't get a good mix (and have had issues with that before). In the case of epoxy, you are adding at least 1/3 as much hardener so even if you mix up to the thickness you want, it's going to get diluted with the 2nd part of the mix.