thin spot in uterus

So as terrible as this might sound, and more than I'd like to admit, one of the big reasons I got on board with having a second (and last) child, is to have a second chance at the natural labor and delivery I wanted with my daughter. I did everything perfectly with her, but her cord was wrapped around her shoulders and with no attempt at alternative, they pushed for a c-section. My husband really wanted our daughter to have a sibling, and I mostly agreed, though I thought I could also be perfectly happy with just our sweet girl. 
Now I'm 24 weeks and they've spotted a thin spot and I have to have monthly ultrasounds to make sure it doesn't get thinner. I'm really down thinking that I'll probably be forced into another cesarean. 
And a fleeting thought, a part of me I hate, thinks, "what the hell was the point then?! Just to be cut open again for a baby that's just going to cut into my time with my baby girl!" 
 I hate that I feel that way and know when I meet my son it won't matter how he came into the world, but I'm honestly crushed. And irrational as no one said it means another c-section necessarily and I'm just jumping to conclusions. 
Plus scared. What if I push for a natural birth only to have my uterus rupture and die, leaving my children without a mom and husband without a wife.