Your excuse of being is homeschooling is ridiculous. I've taught my kids at home for over 17yrs, starting year 18 in Sept. We are very busy from sun up to sun down. If you are sitting down all day then it is your own fault. Studies show kids in public school sit more than people in an office job. You have plenty of things to do if you put your mind to it.
This is an example of one of my teens days-
Get up early at a chosen time usually around 8:30am and start school work.
Walk around the block at 10am before going off to be a mother's helper at neighbors home
Return home and work 2hrs on school work
Volunteer work at church, church members home or another place needing help
Return home for supper finish any needed school work
Relax till bed time
This is just one day. It changes throughout the week to include homeschool co-op, sports, additional volunteer work, random landscaping business that comes from the family business, deliver Meals On Wheels, help out church Awanas plus additional work or help needed somewhere else.
You claim there is nothing to do but have you looked outside your front door? There is a whole big world out there. The joy of homeschooling is you set your own hours. My youngest son is 17 and will soon start working 6 hours a day each week, he is also responsible for his expected school work when we start back homeschooling.
My other teen (my daughter, son's twin) who is the mother's helper at times revolves her school work hours around other things she loves to too which includes volunteering at local pet rescue shelter. She also helps out for some pay at a nearby retirement home.
Look up local co-op groups, most areas even rural one (we live in the country) & you should find one nearby. Our closest one is a little less than 30mins away but we never let that stop us. Ask around neighbors if they need help with any housework or odd jobs, join local clubs, join a sports team and so on. Your options are endless because you are not stuck in a school building all day long.