The Magellan Extreme Adaptive Optics (MagAO-X) is a visible-wavelength adaptive optics (AO) instrument optimized for visible light coronagraphy and exoplanet imaging with the 6.5-m Magellan Clay telescope in Chile. Extremely large telescopes such as the future Giant Magellan Telescope (GMT) will be able to image earth-like exoplanets, given an extreme AO system - such as MagAO-X - exists. MagAO-X is now under development in the lab and undergoing final integration and testing. Technical first light is planned for early 2019, with final commissioning in late 2020. A crucial component to MagAO-X is the "K-mirror," a 3-mirror system designed to rotate the optical field with minimal image wobble or distortion about the optical axis. The K-mirror rotates on a miniature motorized stage to stabilize the pupil in the coronagraph as the telescope tracks the sky. The optical design of MagAO-X required a very compact K-mirror, resulting in a challenging opto-mechanical mount design. We present a novel solution to the compact design of a 50mm max envelope K-mirror for MagAO-X that consists of three < 1-in diameter flat mirrors, all precision glued in place. The K-mirror mount was designed in Autodesk® Fusion 360™ and a prototype was built in the Steward Observatory machine shop. Using inexpensive COTS mirrors, the K-mirror prototype was tested, aligned, and glued with optical feedback in the lab. Once the prototype had proven successful, a final K-mirror mount was fabricated and assembled with invar and precision (0.1nm rms surface roughness, super polished, λ/40 PV flat) mirrors to develop a compact Kmirror for MagAO-X. The performance of the final hardware is presented here.