Just one more thing to add to MinnFlyer's great response.
You may want to seal the gap with tape or clear monocote to get better reponse and help eliminate flutter.
When sealing the gap, be sure to follow the contour of the fixed surface and the control surface edges and not just go straight across the joint. If you seal the gap straight across, you will restrict the movement of the control surface.
Maybe MinnFlyer could add one of his great drawings to this to clear up what I'm trying to say.