Welcome to the Wefugees Community and thank you for reaching out to us.
I think you are in a quite complicated situation and I would highly recommend to contact a refugee counseling office. You don’t have to worry - these offices work free of charge and confidential. They wouldn’t report you to the authorities, for instance. They may also be able to recommend you an experienced lawyer as it won’t be easy to solve your issues. You can use this search engine to find such an office close to your current location.
Getting married officially in Germany is only possible at the registry office (Standesamt) and you will need to submit a number of documents (including your passport, birth certificate and a proof that you are not already married). This process can get quite complicated as well. Furthermore, the registry office may contact the authorities/immigration office during the procedure. Subsequently, the authorities would learn about your illegal stay.
Sorry that I can not give much of a general advice here - it’s very important to get some individual counseling now!
In any case, please don’t hesitate to get back to us with any further questions.
All the best,