OK, there are a couple of things.
The first thing is the issue of what you call this ornament. IMO this isn't really that important so whatever your teacher says.
Second, the issue of "urtext". Urtext isn't really a pure original version of how the composer wrote it. For one thing, it was composed by Petzold and we don't have the manuscript only what Anna Magdalena Bach copied into her notebook and the way she wrote it down isn't how you would in a modern edition (if you're curious here is what that page looks like in the manuscript). When an editor looks at the sources (sometimes there are multiple conflicting sources) they have make decisions and what you get in the "urtext" is only a best guess of what the scholars think the composer intended.
Third, the issue of ornaments in baroque music. There isn't any correct way to play ornaments. All we have is a certain performance tradition. But different people have different ideas and you hear many versions. Also, the ornaments that are written in are just the most basic ones. Most performers add more ornaments in other places according to their taste. It's generally considered tasteful to play the basic ornaments on the first play through and add different ornaments on the repeat.
Anyway, I got a bit carried away nerding out on this topic but I think at your present stage following your teacher's guidance is the best you can do. Just keep those things in mind for the future.
