Was the bagel with jelly, milk and banana for one
meal? If so, actually, your calorie count on it seems rather
low, but that would depend on what kind of jelly you had, and what kind of milk you had (low/no fat, 2% or whole milk).
If you don't mind a quick explanation? First off the bagel is loaded with, both refined flour (unless it was whole grain-doubtful) and sugar, so it's a lot more simple carbs than you should have in a single meal. Secondly, the jelly is mostly sugar.