PDF and CDF using central limit theorem

I am struggling to plot the PDF and CDF graphs of where using central limt theorem where n = 1; 2; 3; 4; 5; 10; 20; 40

I am taking Xi to be a uniform continuous random variable for values between (0,3).

Here is what i have done so far -

clc
clear all
close all
%different sizes of input X

N = [1 2 3 4 5 10 20 40];

%interval (1,6) for random variables
a=0;
b=3;

%to store sum of differnet sizes of input
for i=1:length(N)
%generates uniform random numbers in the interval
X = a + (b-a).*rand(N(i),1);
S=zeros(1,length(X));
S=cumsum(X);
cd=cdf('Uniform',S,0,3);
plot(cd);
hold on;
end
legend('n=1','n=2','n=3','n=4','n=5','n=10','n=20','n=40');
title('CDF PLOT')
figure;

for i=1:length(N)
%generates uniform random numbers in the interval
X = a + (b-a).*rand(N(i),1);
S=zeros(1,length(X));
S=cumsum(X);
cd=pdf('Uniform',S,0,3);
plot(cd);
hold on;
end
legend('n=1','n=2','n=3','n=4','n=5','n=10','n=20','n=40');

My output is nowhere near what I am expecting any help is much appreciated. ( I am really new to Matlab)

[Dheeraj Singh]

Can you elaborate more about what was your expected output and what output did you get?