You can scale the window however you wish, as long as the game still follows the 64x64 grid resolution. If this means making sprites larger (like 4x4 sprite to represent a pixel), then that's fine. Remember though, doing it like that means you'll have to snap everything to the 64x64 grid so you're not drawing at sub-pixel positions.
There will be a category for user to vote on that determines authenticity. This is basically a way for people to say how well you handled using the 64x64 resolution.
Also, what's the tool you're using? I'm sure there will be a more elegant solution than scaling your sprites. Try Googling your tool and "pixel-perfect scaling" or "scaling pixel-art" and I'm sure you'll find a solution. :)