I am married and my wife is from Brazil too like myself. She tells me that she's noticed that a couple of native speakers have "corrected" her when she says "if I were".

I learned that "if I were" is called "unreal" (or subjunctive for Portuguese speakers).

This link explains it in more detail: http://grammar.quickanddirtytips.com/subjunctive-verbs-was-i-were.aspx