There are two things to address before publishing your work: ownership and originality.
Ownership is addressed in the chapter on copyright, originality is addressed here.
There are two caveats to calling a finished piece of music an original composition:
A repeatable composition can be performed again and again by yourself or by someone else. A score is evidence of a repeatable composition. An audio recording is also evidence.
A unique composition is trickier to define. One factor is precedent, the likelihood that a similar piece of music already exists. A composition consisting of a single sine wave is not unprecedented, it is highly likely that a similar example already exists. Another factor is length, the longer a piece of music is the more likely it is to be unique. There are counter-arguments of course. Nearly all the audio in this guide is unique yet much of it is short, and long music may be long because it is repetitive.
Plagiarism, copying the work of someone else, is particularly troublesome. Many of us are influenced by other writers and performers and this will undoubtedly affect our style and what and how we write. As long as we do not mimic other musicians and plunder their ideas wholesale, then a style of our own will gradually develop, which will be unique, and the writing and the music will be unique too.
Ownership and originality may be of no concern to you. You may just want the world to hear your opus. If so, then, as the Duke said, publish and be damned.