Well if you can bump it up to ABB that would give you an IB score of 30. You may want to contact some German universities and ask them if they would consider you with various combinations of grades/subjects, for example they might prefer you to drop Maths and do better in Physics than show up with an ABDD or something. Also an EPQ (I just looked this up btw as I did Advanced Highers, which almost all have dissertations :P ) is meant "to stretch the more ambitious scholar", so idk if that would be any good for you except in something like English, which you're already doing well in?
You should also look up the Numerus Clausus (NC) thing they have going on in Germany, as I think you might need it to study Psychology (sorry, forgot about that in the last post). It's quite complicated, so you might want to ask any universities you're interested in if they would want you to sit that as well and what mark they'd want for it? They'll be more helpful than me on that one I would think! DAAD should also be able to help with enquiries and the English of their admin team will probably be better ^^