iWatermark App for Windows

Does anyone use iWatermark? I downloaded it for Windows 11 but when it opens, it does not give the option to fill the screen. It appears as a 2.5" x 2.5" square, too small to use. No amount of searching has found how to make it fill the screen and it does not enlarge manually. Because of a group that I'm joining, I have to use this app. I will appreciate your help!