It keep auto change my product's size

I am always trying to do newsletter through adobe express, but it will change my page size from flyer to a wide size, I don’t know why it happens, and after I notice this I was trying to find a “save” button or things like that, but it wasn’t work at all,,,,, and I tried to resize it back, but it will change everything. So pleaseeeee, if adobe team can help me fix it