You, congratulations on getting this prestigious scholarship. Your application must have been a strong one, and you should be proud. However, I would echo what Nall-ohki said: this is one of (if not THE) best scholarship available, and many students really want the opportunity. If you feel that you are not truly motivated to go, turn down the scholarship. The Monbusho will offer it to someone on the "alternates" list, and that person will be delighted.
Learning a language is about more than talent or opportunity: it's about motivation. If you don't want to do it, let someone else have the chance.
Good luck with your decision!
Indisoko