No, I mean something like:
plot(x, y, color="blue")
plot!(reverse(x), -reverse(y), color="blue")
PS. Your posted code is not runnable because you didn’t include all of the parameters. I just picked some values at random. Please read: make it easier to help you
PPS. Beware of the habit of using global variables like R1 in your functions. Not only are globals problematic for software engineering in general, they typically lead to slow code in Julia.