I knew these would be too big for my smallish teeth to begin with, but it was still a little tricky to fit.  After trimming them down with a nail file, I mixed the paste and fit them as directed -- they were ok, but not particularly snug.  Pulling the finished paste out I remixed a batch, careful to apply more of it at the back and sides this time.  That worked like a charm and they ended up looking really nice, very comfortable to wear.