Learn English – on the top or on top

The preposition within has nothing to do with the ordinary sense of the preposition with = “accompanying, alongside, by means of, etc.”. Within means “inside” in spatial, temporal and figurative senses.

The hoard was discovered deep within the mound.
You must respond to this communication within thirty days.
They are within their rights in refusing to be interviewed.

Consequently, within is not a valid translation of German in in this context. However, English does support both German uses: you may use either with for mit or in for in.

With this option ...
In this option ...

• HISTORICAL NOTE, for those who wonder why the compound with + in has this meaning:

  Old English wið (cognate with German wider) originally meant “against, by, back from”, and the modern sense of with was expressed by mid (cognate with German mit). In the later part of the Old English period, however, northeast England was occupied and to some extent settled by speakers of Old Norse dialects, and over the next centuries (down into the Middle English period) many Old Norse words replaced the corresponding Old English words. For instance, they and are are of ON origin. Old Norse við, a cognate of with and wider, had approximately the sense of mid and mit, and under its influence, with shifted to the modern sense. However, the old sense lingered in established compounds such as withstand (stand against), withhold (hold from), withdraw (draw away from)—and within (against or by the inside).

Someone is only a "student of" a broad field of study, not an individual class. If I say,

I am a student of philosophy.

Then that means that I am generally interested in philosophy. It doesn't necessarily even mean that I'm pursing a formal degree in philosophy, just that it is one of my personal interests. (Aside: If I wanted to say that I was formally studying philosophy, especially as a degree major, I would say, "I am a philosophy student.")

If you are taking a class, then either in or from is appropriate:

I am a student in your Ethics and Metaphysics class.

I am a student from the Tuesday/Thursday section of your PHIL203 class.

In is probably more common.

To answer a question in the comments, you are never a "student on" a class. You can be a "student on an exchange program" or a "student on leave," but on is never used with a class or a subject as the object of the preposition.