To "get mixed up" means to confuse two or more ideas in your mind. Usually when you "get mixed up" it means that there are choices that you make a mistake and accidentally switch. For example,

I got mixed up and took Highway 50 South instead of North.

You tell what you did when you were confused with the phrase "and (did something)":

They must have gotten mixed up and tried to use Version 2 instead of the newer version.