how can i creatively present the examples of perfect competition and monopoly in my class teaching session?
Your use of the word "perfect" is what makes this tricky. I would have suggested that you divide them into groups and give each group the exact same supplies (perhaps things like strings and beads, or popsicle sticks and straws--whatever would require creativity and innovation, which you could also teach). Have them create their product(s) and then sell them. Monopoly is a bit more difficult to demonstrate here, but if the groups are small enough--or if you have enough of them--they could have the option somehow to buy others out in order to acquire more supplies, to create more products, to sell...and the cycle continues. The groups with the best products would eventually swallow up those which were the weakest, assuming their supplies were still usable to create or enhance the better product. Have fun with whatever you do!
I think it would be hard to do this in a way that would be interesting and yet more effective than simply presenting the information.
I suppose that you could give many people in the class a homogeneous product to sell and let them set their own prices for the product. They could try to persuade others to pay more because their product was better (as in monopolistic competition). This would presumably fail if you make it clear enough that the products really are homogeneous. I don't know how you would make the results matter enough for people to take it seriously, though.
For monopoly, I would think the main point would be to illustrate the monopolies cannot just charge any price they want (that's the main misconception my students tend to have). Again, you could do this by trying to have people sell products. I have the same issue as with the perfect competition -- I don't see how you make the "buyers" take it seriously enough...