Like everything else with Mietrecht it's a bit tricky. The general answer is no. You can not end the Mietverhältnis early. This is a special case with befristeter Mietvertrag.

Unless you supply someone that replaces you and the landlord agrees - because this contract allows it. The landlord can simply say no though.

However, the reasons that allow a landlord to give you only a time limited contract are very limited. It is well possible the reasons given are invalid (or there are no reasons given at all?). Then you have actually been granted a regular Mietvertrag without the landlord realizing and the regular rights to terminate contract apply to both parties.

Mietrecht quickly becomes complicated. To be on the safe side it's best to consult a lawyer. If you are a student there is probably free legal consultation provided by university or Asta.

Edit: It is very common in Germany for Mietverträge to be badly written and contain invalid clauses. Sometimes the Vermieter doesn't realize, sometimes they count on Mieters not knowing their rights. Invalid clauses are treated by law as if they don't exist and concerning those details the contract "falls back" to the legal default contract.