Fitting a PNG image to default playing area size

Hello everyone. I’m an old hand at playing games with VASSAL. But this is my first time designing a module. I’m working on make a module of a card game that incorporates a game board and some miniatures as well. My problem for today is getting my map board image to fit the default playing area exactly. I have it rotated the way that I want it. But I can’t seem to figure out how to make it fill the default playing area. I’ve looked around to try and find a way to set the height and width. But not only cna I not find that option I also don’t know how big the default playing area is anyways. Any help with this would be appreciated.