You should contact a United States accountant and tax lawyer immediately and talk to them. I'd avoid email, and instead stick to using the telephone. You're not entirely up shit creek--many countries have taxation treaties with the United States that lessen the burden to those who have to pay double tax, though I doubt it applies in your situation.
I should also mention that your friend is, from what I can see, liable for you.
I am not a lawyer. Please, seek professional advice!