This logic is not quite correct. One way to interpret your question is to imagine your life and afterlife plotted on a number line. Let's say the "life" portion goes from 0 to 100 (years) and the afterlife portion picks up after that and goes to infinity. Your claim is that if you picked a point at random on the graph, the probability of it being in the "life" portion rather than the "afterlife" portion is vanishingly small, whereas on the graph where only the "life" portion exists, the chance of picking a point at random within the "life" portion becomes 100%.
Let us assume that you are only able to ponder the mystery of your own existence on an internet forum during the "life" portion of your graph (no computers in the afterlife). Then the point being picked is not random, and since it is not random, you cannot infer probabilities from it. (The difference here with the simulation argument is that the simulation argument imagines a very large number of "life"-like regions, only one of which is not simulated. You could be --apparently --posting on a computer in any one of those regions, since they all imitate life.)
I'll offer an analogy to support this claim. Imagine you have a recording that is 3 minutes long. After you play it, it will auto-destruct. Somewhere in the middle of the recording is the statement "This is the moment." When you play the recording, it lasts for a finite amount of time. After that, there is (potentially) an infinite amount of time in which the recording is never ever played again. But there is nothing impossible about there being a specific identifiable moment in that finite time when it was playing, even if there is an infinity of time when it is not playing. (This is actually the same argument as outlined by Eliran and Era, just presented in an easier-to-understand way).