Today, I "upgraded" to VMware Workstation 12 Player 12.1.1 build-3770994.
My problem appears to be similar. The guest operating system is a small box in the middle of my 3000x2000 display, and nothing I can do makes it stretch so I kind have some kind of larger screen for my guest.
It was not this case prior to my upgrade. There was always some combination of minimize, resize, restore down and maximize on the VMware Workstation Player 12 window that would get my Guest to expand to take up more of the screen (and full screen, if I click the VMWare icon for that). But, with 12.1.1, small screen surrounded with at least three inches of black on each side.