There is repetition in your data, 1st and Last row are the same.
%plot upto 2nd last row
plot(data(1:end-1,1),data(1:end-1,2))
xlim([-pi pi])
xticks(-pi:pi/2:pi)
xticklabels({'-\pi','-\pi/2','0','\pi/2','\pi'})
pbaspect([ 1 1 1])
grid on
xlabel('rad')
ylabel('mm')
