Your statements did incriminate you to some degree and probably will result in more in depth investigation
since you gave what the FBI would likely believe to be false or incomplete information. From my experience as a former prosecutor, they do not believe that some random person gave just you money for no reason and with no strings. From this point on, if I were you I would not make any more statements to them without the advice and counsel of an attorney. You can refuse to speak to them any further. It is good that you refused to make a written statement or take a polygraph. Although the polygraph could not be used against you in court
, it still would have given them more information then you want them to have without an attorney's participation. For whatever it's worth in the future never speak to law enforcement if you believe that you are being investigated without speaking to an attorney first.
There is a chance that your attorney can challenge the circumstances under which you gave your statement, but you have to assume at this point that it can be used against you. If you change your story now, you better have a good reason why they are different because the question for you will be "were you lying then, or are you lying now." I know that seems harsh, but that is the way it works.
If you found cash and didn't report it, then you would really only be guilty of not reporting bringing more than the statutory allowed amount of money back from overseas. That is a much lower level of crime than accepting a bribe or money laundering. My recommendation to you, is that you consult with a local criminal
defense attorney who handles Federal cases, as soon as possible. That way you can discuss all the details with them and prepare for any subsequent requests, etc. from Federal law enforcement.