Matlab,normal curve,third power polynomial

Hello, i'm new with matlab and i have a problem with my code, i got this

y=[70,73,62,67,70,72,67,72,71,73,70,75,66,69,67,72 ,67,69,71,71,68,74,73,62,65,75,67,64,72,73];
max(y);
min(y);
bins=min(y):max(y);
numel(y);
x=0:1:29;
numel(x);
polyfit(x,y,3);
best_y=(0.0011*x.^3-0.0499*x.^2+0.6198*x+68.0076);
plot(x,best_y);
u=mean(y);
s=std(y);
normal_y=30*((exp((-(x-u).^2)/(2*s.^2)))/(s*(2*3.1416).^(0.5)));
plot(x,best_y,x,normal_y);
my first tried was with the third order polynomial and then i tried it with the second order one. when i got the graph it looked like 2 parallel lines , i know they have to be close. i dont know what is the problem with my code

the curious part is that when i plot the best_y by itself it looks good upside-down parabola) , same with the normal_y which looks like half of the normal curve. but as soon as i plotted them together one is on top semi-curve and the other one is a line at the bottom. is that ok ?

thanks a lot


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