The phenomenon of non-reciprocal critical current in a Josephson device, termed Josephson diode effect, has garnered much recent interest. It is typically attributed to spin-orbit interaction and time reversal symmetry breaking in these systems. Here we report observation of the Josephson diode effect in a three-terminal Josephson device based upon InAs quantum well two-dimensional electron gas proximitized by epitaxial aluminum. We demonstrate that the diode efficiency can be tuned by a small out-of-plane magnetic field and electrostatic gating. We show that the diode effect in this device is a consequence of artificial realization of a current-phase relation that is non-2π-periodic.These Josephson devices may serve as gate tunable building blocks in designing topologically protected qubits. Furthermore, we show that the diode effect is an inherent property of multiterminal Josephson devices. This establishes an immediately scalable approach by which potential applications of the Josephson diode effect can be realized, which is agnostic to the underlying material platform.