Hey There,
When shooting greenscreen footage where your camera moves, you should ALWAYS have markers on your greenscreen so that when your in AE, you can easily track the shot and apply it to the background on which you are going to composite to. But in this case which you don’t have markers, set a Scale keyframe EXACTLY when the footage begins to zoom in and scale the background to match the footage as if it was really tracked. I suggest using an exponential scale for more realism by right clicking on the background layer and choose “Keyframe assistant” and then “exponential scale” but that is only available in the Pro versions of AE.
Well hoped this helped,
Joey