That looks like the 2D panel.
Try "Shift + 1" or "Shift + 2" to close it.
When you put the cursor over the line between the two, if the cursor changes, left click and drag the window to the bottom of the screen
Sorry, I don't recognize which P-38 it is.
If it is a portover from FS9, you may need to load it after first loading one of the default planes, the Cessna 172 would be a good one. Make sure you are in the 2D cockpit of a default aircraft, then load the P-38.
It may be defaulted to open automatically. If that is the case, it can be changed in the "aircraft.cfg" or panel config. Sorry, it's been awhile but I'm sure it's one of the two.
Good Luck!