Is this too many calories?

I'm 15, 5'3 and weigh about 115-120 pounds. I'm worried about weight gain since I have gained a few pounds in the winter..and I want to burn it off but it's too cold to do any physical activity outside. It's like -25 here everyday. I've been trying to take the stairs instead of the elevator (i run up and down eight flights of stairs everyday) and after school I usually walk around the mall or walk somewhere for about half an hour. Is this enough exercise to prevent me from gaining weight? I will increase it in the spring because i'm joining the badminton team and am going to start walking back from school which takes about an hour everyday. Here's my diet Breakfast: Banana and berry smoothie with half a cup of plain organic yogurt. lunch : 1 bottle of water, a palmful of strawberries and a whole wheat wrap with smoked turkey or chicken . after school snack: a bottle of water and veggies and ranch dressing. Dinner : Some type of lean meat, whole grain carb and green veggie. Snack/dessert: usually 2 cookies and a gl of milk or half a chocolate bar. I have a sweet tooth, and I try to avoid eating stuff like this but I love it. Is this ok?