Here is a code snipped that works, you can get it and modify according to your needs.
Fsim = 5E6; % simulation sampling frequency
Tsim = 1/Fsim; % simulation sampling period
Tdur = 0.1; % duration of simulation in seconds...
t = [0:Tsim:Tdur]; % t = n*Tsim; sampled time instants...
L = length(t); % number of samples in the signal
f_car = 1E6; % DSB-SC modulation carrier frequency
bl_msg_time = filter(fir1(264,0.03),1,randn(1,L)); % generate a bandlimited message signal
msg_dsb_time = bl_msg_time .* cos(2*pi*f_car*t);
msg_dsb_freq = fftshift(fft(msg_dsb_time));
fx = linspace(-Fsim/2,Fsim/2,L);
title(['DSB-SC modulated signal, Fcar = ' , num2str(f_car)])
xlabel('frequency in Hz')
The produced output is:
As you can see the modulated signal is centered at the correct frequency.