Good luck running mommy. I'm sure you'll finish fine, maybe not a PR but that's OK. When I did my first IM and my legs were lead for about 10 km due to electrolyte imbalance, I made little goals for myself on the way and it helped immensely. For example "I'll just run to the next light post, then I'll just run to the stop sign" and so on. Hang in there when the going get tough and set some regular walk breaks for yourself, you'll make it through.

I'll be thinking of you. Try to have fun!