Rear Caliper Adjustment?

[DontPanic]

Just purchased an MX3 and replaced all rotors and pads and rear driver side caliper. When driving the rear passenger side caliper seems to grip the pads too much causing slight braking to occur all the time. Also, the parking brake hardly works on that caliper. When I spun the caliper piston inwards and then applied the brakes it did not reset itself. When you spin it in, does it have to lock in place? Does this sound like my caliper is shot? (Parking brake may need to be replaced as well)