The government would need only probable cause to believe you were committing a crime (possession of 2 ounces of meth does pass this level of proof) and you can be indicted. Respectfully, get a lawyer involved. If they do charge you with conspiracy, you can be charged with all of the crimes committed by the other conspirators, which were a reasonable and foreseeable consequence of the conspiracy. Tell your lawyer everything, including the cooperation you gave, so the lawyer can be prepared to argue these issues in the event that you are charged. Good luck.
Since I do not practice law in your State, this answer is provided solely for informational purposes only, for you to use as a starting point when speaking directly with a lawyer in your State. This answer does not constitute legal advice, create an attorney-client relationship, or constitute attorney advertising. I urge you to immediately contact an experienced criminal defense lawyer admitted to practice law in your State before you make any decisions about this case.
A lot depends on whether you had a written immunity deal. WHile the county cannot give you immunity for Federal crimes, proof that you were acting under an immunity agreement could negate that you "intended" to distribute methamphetamines. The real problem with Federal conspiracy charges is that if you committed one act in furtherance of that consipracy you can be charged for the results of the entire conspiracy. So that is you intended to sell $10 worth of meth and you were supplied that by a ring that was engaged in millions of dollars of meth sales, you coudl be indicted on conspiracy to sell millions of dollars of meth. Talk to a lawyer ASAP