You created a Side Project but used your company's email ID to share it with your teammate at work.

Does that side project belong to you or to your company? If it belonged to you, why would you use office email ID for collaborating on it? and if it belonged to the company, why would you manage it on a personal Trello account?

Sorry to sound harsh, but unless I am missing something, to begin with, looks bad judgement on your part.