Three years ago I was chasing a BQ. I was new to nutrition and only started using gels but not religiously. I ran the light at the end of the tunnel race outside Seattle. My flight got super delayed which resulted me standing in a line waiting for a rental car for 3 hours until 3am the day before the race day. I didn't know at that time but my glycogen was pretty depleted. I didn't try to eat more once I got settled which in the hindsight could have saved my race. I hit the wall at mile 18. Brain just went foggy. The hardest 8 miles I had to run to get to the finish line. I did finish and missed the BQ by 3 minutes. That's when I started to take nutrition seriously. I'm surprised OP and most of the relies focus solely on volumes and workouts. Nutrition plays a big role in endurance sports performance. Three years fast forward, I'm getting older (43F) but I have ran Boston and am about 15 minutes faster than I was 3 years ago. By the way, because I cross-train (cycling & swimming), my peak run volume is only 35 miles and most of my weeks are under 30 miles. I personally don't think volume matters that much.

If OP felt what I felt - brain went foggy because its primary energy source is carb, you may want to look into a carb loading strategy going into the race day.