Did I eat too much today? :/?

You really didn't eat a lot at all. You are a (thin) teenager and do not need to think about having eaten too much, there's plenty of time for that when you hit 60. ;) You should incorporate some vegetables and fruit into your diet, have eggs or cottage cheese along with your cereal at breakfast and have a snack between breakfast and lunch (a cheese stick and an apple, half a sandwich, trailmix, carrot sticks and ranch, etc.).