Start by extending the top surface of the wing to where it almost touches the top of the flap. That will be between the 3" & 3-1/4" location on your tape measure.
The angle from the lower surface of the wing up into the flap cove area looks to be a fairly sharp 90 degree bend. This wants to have a large radius in the 1-2" range to minimize turbulence. Then it wants to slope back in a lazy S shape clearing the leading edge of the flap and following the flap up until it meets the extension which you placed on the top surface at 3-1/4".
I made mine from balsa wood gluing it on and covering it with fabric. It was shaped by placing sandpaper on the flap using the flap as a sanding block running it back and forth until there was clearance for the entire length. When the flaps are up there is a strip of tephlon attached to the underside of this seal used as a rubbing strip for the entire length of the flap.
Piper uses soft aluminum bent at a sharp angle where it almost touches the flap. This is screwed to the top trailing edge of the wing and the flap cove.
When the flaps are down this will give you a slot gap of about 1/2" at the top of the flap. When the flaps are moving down and back this gap will open.
The purpose of the gap seal is to prevent up flow of the air when the flaps are up improving lift in cruise. It also serves the same function as the leading edge slats when the flaps are down by accelerating the higher pressure air from below the wing and redirecting it over the top of the flap thus improving the boundary layer flow over the flap reducing the speed that the flaps stall, improving lift at lower speeds and smoothing the airflow over the tail. This reduces or eliminates tail shaking.