Using green screen with Adobe Premiere Pro, how to prevent floating in the middle of nowhere

Hello. I am a new user of Adobe Premiere Pro. I am recording a talk where I am standing against a green screen, and would like to remove the green screen and put a video in the background. However, when I did this using adobe premiere pro and the green screen feature, the resulting video has me centred in the middle of the video from my waist up, which looks like I am floating and missing legs (in the middle of the video that is replacing the video screen).  Is there a way I can re-position one of the videos so I am not centred in the middle of the background, or change the size of the video that is replacing the green screen so that it isn't so large that I appear to be floating in the centre?

Any advice is greatly appreciated!

Thank you so much!

Emily