This can be caused in two ways.
1) It looks like your project has a 16:9 aspect ratio. If you event clips were shot in a 4:3 aspect ratio, they can be made to fit into the 16:9 frame in two ways. 1) You can letter box. 2) You can crop. You can select these two options in the Rotate, Crop, Ken Burns Tool on the middle toolbar. Crop will cut off the top and bottom of the frame to make it fit.
2) You may have automatic image stabilization turned on. Image stabilization works by zooming in. You can turn off image stabilization in the clip inspector.
Looking at your photos, it looks to me like it is stabilization that is causing your problem. The footage must be quite shaky. In the future, a tripod will cure this. For this project, just turn off stabilization.
Please can you tell me exactly how to turn off the wretched stabilization which has cropped & messed up my video? I've tried opening the 'clip inspector' but it gives no option to remove or turn off the stabilization. Please, please don't tell me I need to re-make all of the projects from scratch; it has taken me days to put together 6 short videos, all of which are now cropped so much they are unusable!
Thanks for any help; I am getting really desperate here!