It strikes me, from your question, that you aren't very experienced in this field so I'm guessing that what you did was replace an existing window. If this is the case then the gap above the window is probably small. Even so, placing weight on top of any window frame is not a good idea. Have you considered using a piece of wood , cut to fit then covered with aluminum facia material? It should match the window nicely and could be furred as needed for thickness.
If, on the other hand, you have already cut a new hole in your wall and installed a window in it, You have already run afoul of at least a few regulatory agencies and would be well advised to cover the what is left of the hole ( and your butt) as soon as possible.