I passed on dessert, only ate a couple of fries, and one piece of bread...but I'm up this morning from Friday.
Just remember that it's 3500 cals to a pound of fat. If your couple of fries and one piece of bread contained 3500 cals, I'd be very surprised!
More likely it's the salt in the bread and on the fries that's causing you to retain water.
Don't *not* enjoy this opportunity because you're stressed about gaining. Go and have fun and taste everything once and just enjoy it. Think moderation, not deprivation.
This is what real life is - sometimes you "splurge" a little and - like you said - keep the mindset that you just don't want to gain.
You'll have a great time and do fine, I'm sure!