I gave myself a deadline ....I wanna break

So I’m going to be 39 in August, and I’m ttc baby #3. I really want a fall baby and I feel like if I don’t get pregnant in the next 3 months ... that’s it ... it over. But the truth is it’s not. I feel like I get too hung up on the idea that I can’t have babies after 40. So many amazing women have babies in their 40s ... so why can’t I? Here’s my fear ... the idea of being 58 when my child graduates High School freaks me out . My mom passes when she was 49 and I have a hard time dealing with the fact I might die and not see my child grow up and have children of their own . To be a grandma. I get stuck in my own head . So do I really give up the dream of baby #3 :( how do I move passed my fears of death .