The incorrect step is 3, that is, molten rocks are heated.
On the basis of Maria, molten rocks are heated up. The statement is wrong as molten rocks are heated up already. During the generation of igneous rocks, these molten rocks needed to get cooled to turn into igneous rocks. The igneous rocks are produced via the cooling and solidification of lava or magma. Thus, the rocks are pushed into the Earth and then they are melted. After getting melted, they come out of the Earth via volcanoes and the lava cools to produce igneous rocks.