Inaccurate course description-- Do I bail?

[XVIIA]

I'm a 1st year PhD student (on quarters) in an engineering field, and I am required to TA in my first year. The spring quarter is super heavy for coursework in my program, and since it's my first time TAing, I applied for and accepted TAship in an undergrad class that seemed very appropriate for my background based on the course name and the catalog description. However, the instructor sent us a copy of the syllabus today, and the course is almost entirely about a completely different topic! All the topics that were explicitly listed on the course description are either crammed into a couple of lectures at the beginning of the class or excluded entirely in favor of topics and techniques in the instructor's specialty. Honestly, these aren't even all that related to the main topic of the class... This is a bit shocking to me since this is a required class with what is typically a pretty "standard" set of fundamentals, but I digress...

Based on the syllabus, I am honestly not qualified to TA this class at all... I have essentially no prior exposure to the "updated" class topic. Even more, it's not even a topic that's even remotely related to my intended area of research, so I don't think I'm even interested in wasting the time to learn it on the spot during a very busy term. I'm not exactly sure how to proceed though... Do I try to talk to the professor and confess that I'm unqualified because the course description was so inaccurate? Do I speak to the coordinator to see if there's even the potential to switch out? Has anyone else navigated a situation like this?