Yes! Completely crazy! Stop thinking about food as bad or naughty & you will stop feeling guilty. 1 piece of cake will not ruin an otherwise 100% week - unless your one piece was the size of a whole cake?
Also, stop thinking about being 'good' all week. It reinforces the 'bad' and guilt, and feelings of deprivation. Just think of it as on plan - & the cake was your syns.