Have you actually organised the rental? Are they happy with it? Do you not need to do some sort of check out before you take the plane?
I mean quite apart from the fact that it will take you a very long time to get to Germany in a C150 from Wick that is quite a sizable trip that even a lot of experienced PPLs would probably seek planning assistance with if they had no international experience.
I'm not trying to dissuade you as such, because with the right guidance it could be done, just trying to make it clear how many different factors there are to consider and be knowledgeable and proficient with before going. There must be someone local who could help you?