You don’t owe a stepparent “Mom” or “Dad.” You owe them the same respect you’d want back.

Names carry weight, and being asked to use one before it is true puts you in the position of faking something in your own house. Nobody is owed that. What is owed, in both directions, is ordinary decency, which does not depend on titles at all. Plenty of people call a stepparent by their first name for years and get on perfectly well.

Use whatever name is honest for now and let it change on its own if it ever does. Be polite, do your share, answer when spoken to. If someone is pushing the title, your own parent is the one to raise it with.