I've been to Winchester a couple of times but don't remember much about it. It seems like it's big enough that you should be able to find ways to amuse yourself other than anticipating the arrival of the new Sonic.
You're much younger than I realized, but back in the day when I didn't have a driver's license, I used an old fashioned method of transportation. I walked or rode a bike, so don't be using that as an excuse for not getting exercise. You can find a way to move if you try.
Also, please tell me you don't consume the crap they serve for school lunch. Bring yourself something healthy from home instead.