MATLAB question I dont think I got it right

Well, you think that it's incorrect, so what do you think the plot *should* look like? Have you, on paper, taken the Laplace transform of the two functions, multiplied them, and then applied an inverse transform?

FWIW, I plot what you have, and it does converge (or at least come down from its peak value to the right of the maxima). As for why it looks similar when you try n0=1000 (and explodes to pretty large values) realize that neither function is finite in length, and thus, neither is the convolution of the two (at least, when you consider the convolution from -inf to inf). By selecting a terminating value of n0, you arbitrarily truncate those functions at those values.

When you ask very specific questions, its often hit or miss as to whether or not someone remembers it right off the bat. I (barely) remember convolutions as I haven't used this in a while. Also, people are usually more inclined to respond to posts that have no responses. By the process of bumping (and bumping several times), people are less likely to respond to, or even read, your post because they see that there are replies.