If you've already submitted an application through USCIS, using the DCF route might not be an option. While I'm not fully familiar with the Nigeria process, a quick online search indicates that some people have successfully taken this route.
I recommend considering a Google search or exploring forums like VisaJourney/Reddit for further insights. DCF can certainly provide a quicker pathway – many people do it under exceptional circumstances like a job offer from a US employer. Some US embassies might assist you even without an exceptional circumstance though (usually for uncomplicated cases without dependents, previous marriages, criminal records, etc.).
A possibility would be to email the embassy to explain your situation and inquire if they would accept your case (after confirming that you meet all DCF requirements; such as the minimum 6 month residency abroad requirement). If they do, you can consider withdrawing your USCIS application and pursue the DCF process (this might be a risky thing to do so you have to take many things into consideration here). Do your research.
I'm not a lawyer, but these are just my personal thoughts; while I don't know the specifics of your situation, I do know the struggles of this process. Hope this helps.