Use of gauspuls command in matlab, unable to broad signal at frequency spectrum

I have a doubt in the gauspuls command in matlab, i entered a fbr(fractional bandwidth of 1.5,ie. bandwidth= 0.75Mhz ) but as i plot the signal in the frequency spectrum using fft. i dont see the signal being broad enough. Why is that. the code is shown below: the below code also has general parameters as follows: dt comes out to be 0.0088us.

%% General parameters %%%

dx=0.05; % mm

Vmax=4.0; % mm/us

alpha=0.99;

dt=alpha*dx/(sqrt(2)*Vmax);% µs

f0=0.5; % central frequency, MHz

t0=1.5; % pulse center time

bndwdth=1.5; % pulse -6dB bandwidth

duration=2*t0; % signal length

timebase=(0:round(duration/dt)-1)'*dt;

[signalI,signalQ,signalE]=gauspuls(timebase-t0,f0,bndwdth);

signal=signalQ;

signal=signal/max(signal);

figure(2)

plot(timebase,signal,'.-')

title('source signal')

xlabel('time (µs)')

fs=1e6;

figure(3)

n=length(signal);

f = fs*(0:n)/n;

Y=fft(signal);

Y=Y';

plot(f,abs(Y))

title('Single-Sided Amplitude Spectrum of y(t)')

xlabel('Frequency (Hz)')

ylabel('|Y(f)|')

Shown below are the plots: