Camera Tracking, Null not tracking

Hi, I need some help here. I'm not so sure what I'm doing wrong.

Here are my steps:

1) Click on Camera tracker, waited for the footage to be tracked.

2) Selected 3 points on a surface, created a null and camera.

3) Placed a Polaroid picture in timeline as another layer, made it 3D

However, the Polaroid does not track.

4) Removed Polaroid picture from timeline.

5) Clicked on Null layer in the timeline and realised that the null was not tracking but stationary throughout the clip.

I've tried pre-composing the footage and it still does not work. Most of the tracking points looks good and fixed on my footage.

My footage is the opening of a door revealing a baby crib and a bunch of stuffed toys in the room. There are no tracking points on the door. Please advise!