There are 3 worlds in A Course in Miracles

Workbook Lesson 128 "The world I see holds nothing that I want." tells us all about the first world. It is the world of FALSE PERCEPTION. This is an hallucinated world added ON TOP OF the manifest world (world #2 below). These are personal, private worlds of ego isolation and insanity. You could say there are as many such worlds as there are egos. This is the same thing as "hell" in course terms. Perceived separation.

Workbook Lesson 129 "Beyond this world there is a world I want." tells us about the second world. It is the world of TRUE PERCEPTION, also known as the real world and the forgiven world. "Now is the last step certain; now you stand an instant's space away from timelessness." .... the "real world" is slightly removed from heaven and the lesson HINTS at there being a world beyond this 2nd world. This is also the world in which we can see a reflection of heaven IN SPITE OF the fact that this world is still an illusion. This is still a world of perception but it's a short distance from here to heaven.

Workbook Lesson 130 "It is impossible to see two worlds." does not yet introduce the 3rd world, but it lets us dwell on the distinction between the first 2 worlds - between false perception OF this world, and true perception OF this world. It has us practice distinguishing or discerning true vs false since this is large part of correcting perception. It also basically tells us that the world we see at this level is what we put there to see, ie we are dreaming this world.

Workbook Lesson 131 "No one can fail who seeks to reach the truth." Finally reveals to us there is a 3rd world, beyond even the "real world" or forgiven world. It is HEAVEN. It is the world that God created. It is your home. This lesson even takes you on a little experimental journey, to go past the world of perception (containing the first 2 worlds), and into the light, accompanied by angels, attempting to bridge the gap to Heaven itself.

3 Worlds. Only one of them is reality. Heaven is reality.