Hi @Harpreet
A sham marriage (in German 'Scheinehe') itself is not necessarily a criminal offence. If a sham marriage results in a person gaining residency rights, then it can be a criminal matter and it is the Ausländerbehörde who have to be informed. However, you write that your marriage is not registered here, which means that in this case it is not relevant for residence rights. If you wish to end the marriage, you can have it dissolved (Aufhebung) or divorce (Scheidung).
I cannot provide legal advice on this and in such a matter I recommend you seek out the assistance of a lawyer. If you are on a low-income, you can apply for free legal advice.
Best,
Éanna