Without seeing a screenshot or knowing anything about the application, it's hard to judge. Usually i would say if 1920x1200 it not enough to display the whole GUI, you need to redesign it. But maybe it's a special-purpose application and all this information must be visible at all times.The issue that I am working on windows 10 with 2880 x 1800 resolution. when I run it on VM or Microsoft surface which the resolution is lower. So the GUI app looks bigger and did not display all its information.
Assuming that you use default sizes for most controls and sizers for the layout, the only thing you can do is set a smaller font. Maybe this reduces the overall size enough so that everything fits into 1920x1200.