iMovie with MacOS Catalina and Logic Pro X file converted to MP3

Hello,

I created a song that I converted to mp3 and saved both copies in iCloud and on my Desktop. I have MacOS Catalina. I would like to make a Youtube video of the song with iMovie, but I get a not enough diskspace error. So, I tried to upload the mp3 song file to Apple Music App, but when I click file then upload (or whatever it says) nothing happens. Meanwhile, iMovie says that there is not enough disk space. This is not true, as my Mac still has 80 some gigs of free memory. How can I fix the memory issue. I read on this forum that you can put the iMovie app in the trash, but do not delete it, then redownload it in the app store, but I don't want to risk it, as then I would have to pay for something that I already have.