@ rbid: thank you very much for your advice. That's a little bit kind of the problem, our profs didn't ask us to do mock- ups or focus on sketching. During my abroad studies for one semester at another university it was way different. But I also think that it is very important, maybe I can do some sketching and mock- ups afterwards....
@ yo: Thank you very much for your advice, I will work on my portfolio again and consider these points. Also it was motivating to hear about the good aspects of my portfolio, thank you
After posting this post in "employment" I saw that there was also the topic "portfolio", which suits a little bit better to the topic of the post. That's why I double posted it, but you are right