Should I cheat on my diet?

My diet basically is DON'T EAT JUNK. I've been lifting weights, doing Tabatha, cardio, bodyweight and yoga. And I'm trying to lose fat my body fat percentage is about 28%. I've been doing this for three weeks.

Today my little brother made the family suger cookies... and I REALLY want some. But I'm on a diet. But I haven't been vary good about my diet (I had cake at a birthday party, I had some KFC when my family got some for supper) and I feel like if I want to see results I can't but I really want some.
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My diet is: I have 3 meals and 3 snacks. Meals I have at least half a plate of veg and at least a quarter protein. And snakes have to be fruit or vegetables.
Should I cheat on my diet?
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