Some artist only topcoat the front, some do the front and sides. When the resin cures it naturally is higher on the edges against the mold.
*After it's removed from the mold you need to sand the top until it's level. Use about 120 grit or a little higher. (If the sides have any blemishes you can sand them too) You don't want your piece too smooth, the sanding helps create a chemical bond between the cured resin and your topcoat.
*Clean your piece, it needs to be completely dust free!
*Tape the sides. (Tape the bottom instead of sides if you're coating the top and sides)
*Topcoat with an Artist Resin, use a torch to remove bubbles.