Re: Nikkah & Fiance Visa information needed!
Applying on GC is painful, but if you are applying your naturalization in June it will take 5 month from June. Its mean, you could eligible in December to claim yourself US citizen if everything goes fine. You can apply I-130 now and change your immigration status in December by calling USCIS.
I think you should call USCIS and ask if it is allowed to change your immigration status on your applied petition.
Edit: Here is PDF from official source. http://www.uscis.gov/USCIS/Resources/B1en.pdf
Please read page # 2.
What if I filed a petition for a relative when I was a permanent resident, but I am now a U.S. citizen?
If you become a U.S. citizen and your relative’s petition has not yet been approved by USCIS, you will need to notify the Service Center where you filed your relative’s visa petition. You should send the notification to the Service Center address located on the receipt notice you received when you filed your Form I-130 petition. Please include a letter with information regarding your relative a copy of your Naturalization Certificate, and a copy of the petition receipt notice. Call Customer Service at 1-800-3755283 for additional assistance or if you are unsure about the status or location of your petition.