Help with pskmod and plotting in GUI

so i'm trying to plot the waveform of BPSK like this in the fig but i only get a straight line

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- Inputs are bitstream , intial phase shift - output is the waveform

here's the code :

if true        
% Start of Carrier Intialization
Ts=1;f=4;
t=linspace(0,10*Ts,1000); 
carrier=sin(2*pi*f*t);
% End of Carrier Intialization
% User Enters the MSG
BStream = strread(get(handles.BitStream,'String'));
symbols = BStream; 
symbols = repmat(symbols,100,1); 
symbols = reshape(symbols,1,1000);
% End of the MSG
P0 = str2double(get(handles.edit2,'String'));  % Intial Phase shift
modSignal = pskmod(symbols,2,pi/P0); %BPSK Modulation
handles.modSignal = modSignal;
guidata(hObject,handles);

end