Need advice gained 12lbs at WDW

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Just got back from a 7 day vacation at Walt Disney world and gained 12lbs even though I was hitting 20,000 steps a day (averaged out at 10 miles) I didnt indulge as much as I could! I didnt eat 3 meals a day but i did have a treat every now and again how did i gain all this weight with walking every day for 10 miles!