I accidentally used cancer donations to buy a video game
That was no accident. Is this going to cause some issues?
Even though it had some side-effects, I think this was the right thing to do...
You should return that money ASAP. There is nothing okay about using cancer donations for things like video games.
If I miss-used their money it's their fault, they should've paid closer attention.
You can't place the blame for an act on the people who were trying to help with an awful situation.  It was your choice to take the action you did and you can't blame others for it.  I'd return that game and take the refund money and give it back,