Here's the specs for your system: MacBook Pro 13" 2.9 GHz i7 (Mid-2012)
Here's what the system is able to support from EveryMac: 1280x800
Apple reports that this system also supports:
- 1152 by 720
- 1024 by 640
- 800 by 500 pixels at 16:10 aspect ratio;
- 1024 by 768, 800 by 600, and 640 by 480 pixels at 4:3 aspect ratio
- 1024 by 768, 800 by 600, and 640 by 480 pixels at 4:3 aspect ratio stretched
- 720 by 480 pixels at 3:2 aspect ratio
- 720 by 480 pixels at 3:2 aspect ratio stretched
Now here's the other shoe falling...
Intel HD Graphics 4000 services can't push two screens at different scaling or ratio's
Now the newer retina class systems offer deeper options MacBook Pro 13" 3.1 GHz i7 (Early 2015) for reference:
3840x2160 on two external displays via Thunderbolt 2, Alternately, it can support a single display up to 3840x2160 via Thunderbolt 2 and a single 1080p display at up to 60 Hz, 3840x2160 at 30 Hz, or 4096x2160 at 24 Hz via HDMI.
This series uses the newer Intel Iris 6100 graphics services.
Even still the internal display is not running in true higher screen resolution depending on your OS version. Here's a bit more on that: 4 Ways to Run a Retina MacBook Pro at 2880×1800 Native Resolution.