Just track your genealogy. Go up like 3-4 nodes from your parents and then expand the tree from there.

The expansion gets even more extreme if you start your expansion further up the tree, as the average number of children per household goes up dramatically as you go further back in time.

https://populationeducation.org/wp-content/uploads/2020/04/a...

Genetically, you're just about as close to your great-great-grandfather as his second daughter's son's third daughter's nephew is.

Unless you've been in some sort of clan war for generations or your family has been the target of small-scale genocide, you're unlikely to be the 'last of a bloodline'.

At a complete guess, that may be inaccurate because I don't know you? What you possibly have is a biological imperative to reproduce, perhaps some social expectation or personal desire to have a family, which combine to create the anxiety. Then the anxiety manifest as magical thinking about "being the last" in a way to drive attention to the underlying issues. Is it 'being the last' or 'being alone' that's the real driver?