Layout Orientation ratio change after bring in Audio on iMoves

I am new to iMovie. I want to make a short for YouTube. I brought in all my photos, transitions, crops, etc. and everything was fine for 9:16. Then I brought in a 38 sec audio and it turned into a 16:9 layout. I cropped a 3 min audio into 38 sec and still changed the ratio. Since I cropped it in Quicktime the MP3 turned into a M4a file. Since I want this to be a short it has to be 9:16 ration. What do I do? Any help is appreciated.

[Re-Titled by Moderator]