You need to see an immigration attorney before you file anything with USCIS. As my colleagues have mentioned, claiming to be a US citizen, even on an I-9 form, can bar you from receiving immigration benefits for life. There is no waiver of this ground of inadmissibility available. Prior to 2009, the I-9 form asked if you were a citizen or national of the United States. So, if you checked yes, the argument could be made that you were only falsely claiming to be a US national. Falsely claiming to be a US national does not carry the same consequences as a false claim to citizenship. The I-9 form now has a separate box if you are claiming to be a non-citizen national, so you cannot make this argument.
Further, it is worth noting that even absent the false claim issue, adjustment of status based on marriage is an immigration benefit only available to individuals living in a bona fide marital union with a US citizen. Having a legal marriage to a friend, without the intent to live as husband and wife, is not adequate.
Finally, you should not post such admissions in a public forum. Such discussions are best had in the privacy of an attorney's office, where the things you say will remain confidential.