I don't think it's necessarily a boss theme, but it definitely has that evil/dark theme. It's sounds like it would be the theme that would be playing right before you get to the boss. If if was a boss theme, it would be more intense feeling when listening to it. It's not bad, and I'm not saying that you couldn't use it as a boss theme. I just felt that the song never really burst out with excitement or with a faster paced theme that would be the chorus of the song. Since this is your first audio that you made, you did an awesome job. I would suggest changing the title, but that's just my opinion (my first songs sucked btw).