Nobody owns the idea. If I knew what idea you were talking about, I could go make a new company based on that idea -right now-.

Copyrights are for art, and patents are for inventions. Neither of those cover 'ideas'.

You didn't sign a contract stating that you wouldn't take any business secrets away from the company, either, I assume, since you say you aren't even incorporated.

Walk away now, start coding for the new company, and don't look back.

I am not a lawyer and this is not legal advice.