boundary condition

I m new in comsol. i m trying to find capacitance of an electronics device . but i did not get exact result. there is little bit difference between simulated data and expected result. i think my boundary condition is not correct..
what type of boundary i have to put ?
i added only Ground and terminal.. after that i don't know anything.
under the Electrostatics(es) ,i am facing problem .

thanks
sandipan