Hello Joe@ thank you for sharing your problem with us, it's only possible if you have your identity card or anything that shows or gives the authority full details about where you come from like your country passport, ID card or birth certificate or if you have German resident permit in Germany . If you have any of these, then the decision have to be make between you and your partner but if you have none of them, then the child have to take the mother surname but not you. I hope i have answered your question and don't forget to come back again to share your questions with us.