The equation is incorrect because it violates the law of conservation of mass. On the left side of the equation, there are three magnesium atoms and two nitrogen atoms, while on the right side, there are three magnesium atoms and only one nitrogen atom. This means that one nitrogen atom is lost in the reaction, which is impossible.

The correct equation for the reaction is:

$$3Mg + N_2 \rightarrow Mg_3N_2$$

In this equation, three magnesium atoms react with one nitrogen molecule to produce one molecule of magnesium nitride. This equation conserves mass, as there are the same number of atoms of each element on both sides of the equation.