Welcome to the Wefugees community and thank you for your question.
This is a tricky situation. First of all, the asylum procedure and the marriage procedure are not directly linked to each other. That's why it can happen that Ausländerbehörde wants to deport you even though you are planning to marry.
The problem is that you need documents that allow you to stay in Germany in order to get married (e.g. Aufenthaltsgestattung during the asylum procedure or Duldung or a residence permit after the procedure). If your asylum procedure ends with a negative result your Aufenthaltsgestattung expires. If you don't get a Duldung you might get deported real quickly especially since authorities already got your passport.
If you have the option to appeal once more, I would do it. It gives you a little more time to wait for your certificate of no impediment to arrive. If Standesamt got all the required documents they can give you a document that states the wedding date. If you can prove to Ausländerbehörde that your wedding is imminent with said document, then they can decide to postpone deportation and give you a Duldung instead. After getting married you can apply for a residence permit.