You seem to have only uploaded the executable file. Instead, upload the whole folder of the game, I don't use Unity, but it's always about 5 files, 3 of which are folders. Put that all into a single folder, zip it and that should work. I believe DuckyDev mentioned that changing the .exe files is ok, but given how easy it would be to cheat, I unfortunately think that you cannot change anything here. But you can update the game after the jam, just to show it up! The artstyle looks nice!