Error in Exact solution and numerical Solution

Hi I am solving a 2nd order linear ODE using Forward Scheme Finite Difference Method and also computing the Exact solution and plot these 2 curves,but there is very much error in my curves. Please follow my code and mention my mistake in either computing forward scheme or some else.

clear all;clc;
  t0 = 0;
  y0 = 0; 
  Dt = 0.01; 
  tn = 1;
  t = t0:Dt:tn;
  n = (tn-t0)/Dt +1;%length(x); 
  y = zeros(1,n);

% Second Order ODE
for j = 1:n-2
y(j+2) = -(1-Dt)*y(j)+(Dt^2)*t(j)*exp(3*t(j))+(2-Dt)*(y(j)+Dt);
end;
plot(t,y,'b:');
hold on;
% Exact Solution
y1=(10/9)-(7/144).*exp(3.*t)+(1/12).*t.*exp(3.*t)-(17/16).*exp(-t);
plot(t,y1,'r-');