adding files together with different stage sizes

Hi there, myself and my friend were both making scenes in separate files which we were going to add together at the end, however we made a big mistake and have different stage dimensions (we're new to this). I tried adding the scenes to a new file when I noticed this, and I tried using the 'scale content' option, however it did not work and looks awful. Is there a way to fix without having to resize after every keyframe does anyone know?