You're working in Godot 4 right? Try setting the itch.io window resolution manually to what your godot project viewport size is!
Also try going to Project > project settings > Display > Window and change Stretch mode to "viewport" and Aspect to "keep". Then upload a new project file with these settings. It will most likely solve the problem.
This has solved similar issues for me in the past!
Test the solution on a separate project draft, just in case.