iMovie's screen aspect ratio is 16:9, and that cannot be changed. It's possible that the Zoom video is not a true 16:9 video, in which case iMovie is cropping it slightly to fit its 16:9 screen.
Open your project and click on your project's name under the heading of Project Media at the top of the sidebar. That will reveal the project media browser screen. Click on the Zoom clip in the project media browser screen to display it in the preview screen. Does it display correctly there? Does anything change in the display when you drag it to the timeline? Now, in the project media browser screen, select the clip and do File/Reveal in Finder. An Original Media folder will pop up with the name of the clip highlighted that you selected. Click on the clip's name to play it in the Original Media folder. Does it play without any cropping at the sides?
What we are trying to determine is whether the clip imports correctly into the finder but appears cropped when imported into the iMovie timeline. If that's the case, try deleting preferences and see if that cures it. To delete preferences, open iMovie while holding down the Option and Command keys. iMovie will open in a new blank library. Reopen your original library to get back to your project. Now open the project and see if the clip displays without cropping.
If no success, as a workaround try placing the clip above a black background in the timeline. Use the overlay feature to overlay the clip as a Picture in Picture. With the Picture in Picture feature you can adjust the size and position of the clip by dragging its corners in the preview screen. See if you can size it so that it properly displays in the preview window without cropping.
-- Rich
-- Rich
In any event,