Hi,
Why don't you use the 'interp' function to interpolate the data and then plot it? Below is an example code snippet from the documentation.
t = 0:0.001:.029; % Time vector
x = sin(2*pi*30*t) + sin(2*pi*60*t); % Original Signal
y = interp(x,4); % Interpolated Signal
subplot(211);
stem(x);
title('Original Signal');
subplot(212);
stem(y);
title('Interpolated Signal');
