Polynome not graphing correctly in R

Question

I have the following code:

 nn =18
 set.seed(5948172)
 x = runif(nn, 0, 2)
 y = 6*x + 2*x^3
 ye = y + rnorm(nn,0,0.6)
 df = data.frame (x=x, y=y, ye=ye); df[1