I think, given what you have said, you are committed to following this through. All I would say is make sure you have written down what you want to say, and have clear factual examples of the issues you are raising. Stick to the facts, don’t make it personal, keep calm in the meeting, and see what happens.

You’ve thought it through, and made a clear, sound choice. Try not to overthink it now, or to worry excessively. I hope you get on ok.