I've done it both ways...admitting it and full on lying about it. If it's one cheat, once and little, nothing earth shaking...i don't tell them. I am pretty honest about my meals, if I eat lasagna, I'll put that in there, but if it's a snack between meals, like a bite of this or that...thats when I don't tell. They don't love when a meal is off, but depending on the consultant they aren't too hard on me. I don't like the consultant that makes a big deal out of me eating two breadsticks instead of one or a half of one. I feel like I"m human and sometimes I'm just not gonna be perfect.
Also...if i'm traveling and am not intending to eat on plan, I tell them that too. They aren't my Mommy, so they can't tell me no, though they discourage it of course. They'll try to sell me a fat/carb blocker, which i don't want (i think its cheating) and tell me to stay on top of my water. I don't keep a food log when I travel either FYI.
If at first you don't succeed...dust yourself off and try again!