Congratulation on your first pieces, they look really good (you should have seen my first one 
), yes you can polish your resin, this is what you do, if the surface is good just a little marred you can go over with 400 grit sand paper and polish it with a good car wax, if the surface is a bit too rough for that, sand it down a little with 220 paper and coat it with shellac, or poly
To spray the mold I use the grilling high temp Pam, sometime the resin will get hot and this Pam works nicely
Again : good work
j