don't want to charge

I work at an LTAC. I've been there for 9 months. I like the work very much, but the supervisors often schedule me as relief charge. My background is mainly home health and med-surg. I worked telemetry years ago. This LTAC often has critically ill patients on vents and drips. I'm learning, but don't feel qualified to charge. I have talked to our lead charge nurse, our director of clinical services and the CEO. I'm told that the staff likes it when I am in charge because I stay calm and try to be fair. Most of the time there is another RN working who can also charge. I feel that this is not right to have me charge when I admittedly tell them that I don't feel qualified. I'm afraid this could have legal ramifications if something goes wrong while I am charging. Any advice on what to do next? Thanks yr of tx.