If its just a bit sticky on top (sticky like youre putting your finger on scotch tape and it sticks to it) versus you put your finger it and can really squish it (like a PB & J sandwich), then you should be able to get away with pouring a thin layer of resin on top.
If you want to try sanding, start with a coarse grit (400 or so) and work all the way down to 2000 grit sandpaper. It will almost be a gloss, but you will still have to cover with a resin layer to get the super shine on top.