Ask god to help me cut the whole picture with matlab. The tangent is correct, but the symbol of the constellation is not in the center. Is there any way to solve it? A novice.

fs = 128； % sampling frequency

fc = 10； % carrier frequency

f = 3； % original signal frequency

t = 0: 1/fs:2；

x = sin(2 * pi * f * t)+sin(8 * pi * f * t)； % original signal

% Double Sideband Carrier Amplitude Modulation

ydouble=amod(x，fc，fs，' amd sb-TC ')；

zdouble = FFT(y double)；

f _ dot = fs/length(zdouble)； % point frequency

zdouble = ABS(FFT shift(zdouble))；

N = length (zdouble);

frq double =(-N/2:N/2)* f _ dot；

frq double(N)=[]；

Figure (1);

Subplots (2, 1,1);

plot(frqdouble，(zdouble))；

Axis ([-30 30-10 279]);

Title ("Double Sideband Carrier AM");

xxx = ydouble