Help with LPF and signal

In our signal processing course we were asked to pass a signal through a lpf that had lower the amplitude by at least 20db at w=200pi but not change the signal at w=20pi the signal is:

Xct=exp((-3)*t).*(cos(20*pi*t)+cos(200*pi*t))

and the filter we built is:

LPF=tf(3969*pi^2, [1 126*pi 3969*pi^2])

we built this filter using the bode function; making sure that the amplitude of the filter alone would be 0db until half a decade before w=200pi.

however, when we pass the signal through the filter, the signal is amplified where is shouldn't be: the code is:

Y=Xcs*LPF; %frequency plane LPFt=(3969*pi^2).*exp(-63*pi*t).*t; yt=conv(Xct, LPFt);

when xcs is the laplace transform of xct. we calculated the laplace transform outside of matlab and entered it with this code:

zero=[-3; -3+i*446.504; -3-i*446.504]; pole=[-3+i*20*pi; -3-i*20*pi; -3+i*200*pi; -3-i*200*pi]; k=2; [b a]=zp2tf(zero, pole,k); Xcs=tf(b,a);

Can someone please explain why the signal is amplified? or if we've done something wrong in the matlab code Thanks in advance