Uploading scores

I’m uploading a music sheet that I arranged.
Perhaps the song that I arranged is recently released so there was nothing on the “choose the composition your score is based on” part.
So I add a new one, I wrote the author’s name and the description carefully, and put it as “not in public domain” (I believe it still belongs to an author).
But when I finally save the score to upload it, the score is put as “public domain”!!!
No matter how many times I tried it won’t let me change to “not in public domain”
What should I do please?