How to convert german undergrad grade to US GPA
You can always call the school to find out.  I'm sure you won't be the first foreign student to have applied.  That said, it looks like Wikipedia has a pretty good page on how to convert, and your score should be somewhere in the 3.75 range or so.  

https://en.wikipedia.org/wiki/Academic_grading_in_Germany

You'll have to go course by course to find the right number.  Good luck!