You can't "flush" out fat, to remove it, it requires healthy eating, staying hydrated and the right kind of exercise, probably not what you wanted to hear.
Abdominal fat is notoriously difficult to get rid of, a tailored exercise plan would probably be the best option for you to lose this excess fat but remember to always talk to a doctor beforehand, they can help with safe healthy eating plans and help to ensure you aren't losing too much weight, only losing the unnecessary fat.
If you are going to college, most colleges have a gym that you can become a part of, some automatically grant membership to students.
On the spell front, you could try a motivation spell, yes the weather is getting colder but if you want to lose the weight and being outside is your only option, a motivation spell is a good option. Spells won't help you lose the weight but can keep your drive to do it, high.
Do remember that weights, running, cycling or other general gyms aren't the only ways to lose weight and build stamina, going to the pool every week with a plan to train can be just as effective, and can be a pay per visit system rather than a monthly or even yearly fee.
I hope this helps.