Do this:
Plan your day out right now (either for today/tomorrow depending what time it is there).
08:00 - 30minute walk (this way, even if you end up doing nothing else, you know you exercised)
08:30 - Healthy breakfast (try your usual fruit plus some cereal and yogurt mixed in)
09:00 - Spend some time doing something you enjoy (a hobby or exercise)
and so on and so on...
Is the problem maybe that you have nothing to do now that school's out? What options are available to you for entertainment during the day in the week? Do you have a friend that will join you in getting healthy... maybe walk with them, or organise to meet at your place or hers and do your exercise tape together.
Start a project for the holidays. Maybe you want to spring clean your whole room. Break it down and do a section each day. Maybe try and incorporate a set beauty routine for the week... face masks, foot scrubs, your own manicures and pedicures, as well as body brushing can all be done on certain days once a week. This helps for me as I love pampering myself!
Another plan is to attack the food head on! Find some cool recipes that you have the ingredients for (and that are deliciously healthy), then get busy in the kitchen.
Do you have a garden? Planting herbs to use in your foods is great... plus gardenings a bit of exercise! And what about tanning and swimming??
Also make sure you don't slack on water... get those 8 glasses or whatever in. And your veggies, you'll start feeling sluggish if you don't keep your healthy habits up now!
Maybe now is also the time to investigate some strength training... find some body weight exercises you can do in your room... then do them in front of the TV!
Phew, I hope you find something in there. And remember howe excited you were about having free time to focus on being healthy!?
Good luck (but you don't need luck, just do it!)