Writer's Fallout Shelter

This is something I've recently come across that has deducted me a few points within a contest.

When it comes to writing in the first person, how do you convey that the character is not you? I recently entered a contest where the flash fiction was in first person, and everyone automatically thought I was writing about myself instead of just from a character. The story was in no way tied to me except that I was the writer. It irked me quite a bit that I was being docked points because of this. They said it was so touching seeing me relate my story to the contest, basically, but they couldn't relate to the character/me and made a point to say that they thought it was me, mentioned that the personal life got in the way of the plot, and that (because of the personal reference) the plot wasn't very original. I wouldn't be coming here, however, if it only happened once; it happened at least twice with the same piece.

So I'm asking anyone who is willing to answer, please. When it comes to short pieces in first person, how do you distiniguish between you and the character? What does it take? An author's note? A better description? How do you do it???

I figured I could post this now because it ties with the fact or fiction thread we had going but deviats a little...