I'm wondering if there's a way to just link my song through soundcloud, without having to create a project?

(btw i already finished it lmao)

I am afraid not. Just as any other game jam, you necessarily submit a project page with the required content in it. You can still link your song through soundcloud (in the "Streaming Service" option when submitting, or in the content of the project, or both!), but there is no way to submit just a soundcloud link.