Hi Leo,
Resin poured onto a flat surface will always give a glossy finish assuming it is mixed properly. If you want something either than the gloss finish, you can go over the surface with wet/dry sandpaper. Something in the 400 to 600 grit range will give it a matte finish, while 800 to 1000 grit will give it a satin finish. I would suggest testing a few pieces with sandpaper first to see what you like.
Good luck!