Trust me on this one, if you wanna take away the sheen then throw some dirt on it lol. Bro, I use Matte finish and you still cannot see it in the sun till you are within boulder tossing distance. If you are really worried about it I would either use a real fine sand paper lightly on it or just dust it VERY lightly with the ultra flat. Either way I would suggest trying whatever you do on a smaller removable part of the rifle first so if you arent happy with that method it wont be too painful to start over or try again.
And Welcome to DIY Weapons and Gear Customization. Even after doing this... oh about a dozen and a half times I am still learning new things! Don't let a little set back (if it really IS one) bring your spirits down.