Ford Mustang disc brakes

I replaced the rotars and pads on my 2004 Ford Mustang Convertible about 3000 miles ago.

They work fine but I recently heard a small squealing noise.

The drives side rear disc pad is not making complete contact on the rotar facing the underside of the car.

I took it apart and the inside pad seems to move freely and not stuck.

The inside rotar surface is rusty about half of contact area towards the outside of the circle.

The parking brake seems to be working and the cable moves when applied.

What is wrong and what do I need to do the repair it?

THank you,

Gene

Did you put brake grease on the backs of the pads before you installed them, as well as confirming they are the correct size by comparing them to the old ones?

Try operating the parking brake several times. Doing this is what adjusts the rear disc brakes for pad wear.

Tester

I did put the grease on the areas that the pad would move.
The pads did look the same size. The pad on the other rear wheel are working okay.