Using FFT for linear convolution in frequency domain

I am trying to find the system response given a periodic input (in this example it is cos(t)) I have an impulse response, h and an input force, f.

My code works, but the plot is incorrect! the amplitude is way off of what it should be, so i believe i am using fft wrong.

Please help me find my error!!

clear
%system parameters
m=4;               
k=256;                 
c=1;

wn=sqrt(k/m);
z=c/2/sqrt(m*k);
wd=wn*sqrt(1-z^2);
w=sqrt(4*k*m-c^2)/(2*m);

x0=0;   %initial conditions
v0=0;
%%%%%%%%%%%%%%%%%%%%%%%%%
t=0:.01:10*pi  ;%time vector

f=cos(t);   %force f
F=fft(f);

h=1/m/wd*exp(-z*wn*t).*sin(wd*t);  %impulse response
H=fft(h);

conv=H.*F;   %convolution is multiplication in freq domain

plot(t,ifft(conv))

I have read things about zero-padding for linear convolution. I am not sure how to implement this, maybe this is why i am getting weird results?

Thanks!