Questions about 1040NR EZ and 1040X

Hello,

I am doing a 1040X and a 1040NR EZ in order to amend a return that I submitted by mistake as 1040EZ through TurboTax when I was on my OPT. One of the questions ask if I filed a U.S. income tax return for any prior year and to write the year and number form. The problem is that I did also Taxes on 2010 because I had a part time job in my university on 2009 but I did my taxes with the help of some volunteers from my university. I don't remember which form number they used and they did not keep any records.

My questions are

What should I do or answer in that question?
What should I write on my 1040X? The only change that I am aware off is the form number.
I am really worried that I can get in big trouble like jail or something for having filled the 1040EZ by mistake when I should had filled a 1040NR EZ. Can I go to jail for having made such mistake? Or Can I just pay what I owe because of my mistake? I no longer live in the US but I would like to correct what I did.

Thanks for any help

Questions about 1040NR EZ and 1040X