Ethics of Accepting Unneeded Merit Based Scholarships
Congratulations! It's your decision, but I think the most commonly accepted point of view is that it's totally fine to keep the money. One thing you could do with it, or with part of it, is to give back to a need-based scholarship fund or to any other worthy cause. 

Also, at least in the US, it is common for universities to solicit donations from alumni, so if you so choose you will have an opportunity to 'pay it forward' after you graduate.

Again, congratulations!