I am investigating the Lorenz equations and in MATLAB I have plotted a case with $\sigma = 10, b = 8/3, r = 21$ and I have this phase portrait: 
However I am not exactly sure how this is an unstable limit cycle. According to Strogatz, this should be a saddle limit cycle. I am also unclear as to why there is that white space on the left cycle. Could someone please explain what is going on here? I think I am a bit lost when it comes to interpreting this plot.