I have a pizza dilemma?

tonight I will have dinner with some friends and they want to eat pizza and it would be rude to say no. what to do? i will eat just one slice. do you think I will gain weight?
this is what i had today:
cereal, unflavoured yogurt, cereal bars, coconut yogurt, fish, salad, peanuts and apples
I have a pizza dilemma?
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