Distorted cutaway image in iMovie
I'm trying to make a very simple countdown movie in iMovie, using .png files as cutaway clips so that I can use my customized fonts & designs throughout the movie. The .png files are saved at 720 x 540 (at 600 resolution) & I'm making a standard (4:3) movie. When I add the .png files to iMovie, the image is immediately distorted (see screenshot). The images remain distorted upon export. I can't find a solution ANYWHERE on the internet - Is it possible that I need different dimensions for the .png images? It seems I'm the only person experiencing this, so I think I am missing something very obvious. Please help!
MacBook (13-inch Mid 2009)