Dear Gentle James,
Welcome back to the Wefugees Community and thank you for being such an active member.
Regarding your situation: I find it quite difficult. Without knowing the individual circumstances or motives, you apparently were not explaining the truth in your interview with the BAMF. I am sure they will be not too happy about it and I can unfortunately not give you any further information if there will be consequences to expect (most probably also related to your current residence permit/status). Apart from that, I am quite sure that the authorities will check your documentation very well before you will be able to marry. Did you consult the local "Standesamt" (registry office) already? They will explain you which documents you need to provide exactly. For an overview, you may want to check our blog on this topic. Be prepared that authorities might also ask for double-checked documents, affidavits, legalisations etc. (i.e. from the embassy or from initially issuing authorities).
I will also link two of our experts: Dear @mbeon-Ruth or @mbe-on_Zsigó, can you give any advice here?
All the best,