is closed? is it supposed to be pressed to the roof your mouth?

Well, probably. l am not sure how much it matters, though if u do not have any neurological problems. You see, u have filliform buds on ur tongue that r not used for taste sensation. They're the structures that allow u to stick ur tongue to food & move it around inside ur mouth while chewing. They also help ur tongue ''stick'' to the roof of ur mouth when ur mouth is closed. So, l would suppose that ur tongue naturally sticks to the roof of ur mouth when ur mouth is closed.

Yes, your tongue is supposed to be pressed to the roof of the mouth.

If you rest your tongue on the teeth instead, your teeth will get flared, because of the unhealthy force produced, which we call ''Tongue Thrust''.