Looks pretty sinusoidal to me. You've only plotted a very small portion, though. Maybe try letting x run from -5 to 5 to see more of the domain?
Also, I think you can let m be something a lot smaller, and you will still see the limiting behavior well.
I notice in your formula you have (-1)^3.14 in one place where the formula has (-1)^m.
Finally, you can use "pi" in place of 3.14. MATLAB understands what that means.