I'm having trouble believing I can accomplish my race pace. What takes over on race day? How do I know I can? What can I do to help mentally? How do I even know I've got the right race pace?

I've been training for a late October marathon and I'm finishing week 9. I've not missed one run. I've most definitely noticed that faster speeds are getting better but I was doing some tempo intervals of 15min at half marathon pace and the entire time I was thinking this is an okay pace right now but how the hell did I hold it for almost two hours. It's messing with my head a lot. I'm also so confused about what I should aim for my marathon pace.

Backstory: Late April I raced my first half where I followed a training plan off and on but pretty strict for the month before. I ended up running it in 1:46 (5min/km, 8min/mile). This blew me out of the water. I knew I could hold that pace for 5km but never in my dreams did I think I could do it for half. I also was just running to finish it and so didn't go in with a pacing strategy but ending up running a very evenly split race.

About a month later I raced 5km and did that at 22:24 (4:29min/km, 7:13min/km). I left nothing on the table for that race but I hear that's common enough for 5ks.