How to modulate with qam?

How do I use the modulate function with the qam parameter? My code is below, but I do not think this is the correct way.

%%Time specifications:
Fs = 737e6;                   % samples per second
dt = 1/Fs;                   % seconds per sample
StopTime = 0.000001;             % seconds
t = (0:dt:StopTime-dt)';     % seconds
%%Cosine wave:
Fc = 30e6;                     % hertz
x = cos(2*pi*Fc*t);
%%Sine wave:
y = sin(2*pi*Fc*t);
%%Resize to first 320 points
x = x(1:1:320,:);
y = y(1:1:320,:);

fmSig = modulate(x, Fc*2, Fs, 'qam', y);
plot(fmSig);