I think I will use the latter which is wider, so it covers it completely, I made few mistake w/ my coop/shed when I was building it but I just reinforce cover it rather than tearing and reassembling as long as it’s not safety frame issue. Here’s my windows except yours will elevated from the wall.
This might work or might had been mentioned already Since you already installed the window, can you frame it with 2x4s? All around to reinforce those channels using screws then hide the white part with thin outside trims so it would look like picture frame elevated or 3D look let me find my...