Fortnite is going to make things a bit better for those who make an accidental purchase on the game's store, or make a purchase they decide they don't want. This information comes from an Epic rep via a Reddit thread.
"Our initial solution for this was to add a refund token system. As an ongoing iteration, we are going to introduce an “undo” button to the store page that allows you to easily refund without using up a token within a 5 minute time window, assuming you haven’t started a match since purchase."
While you won't have a lot of time to undo your purchase, and there's some other limitations put in place, it's still a better option than what's available right now.