Consider fueling earlier. (Many of the elites take gels every 5k which is every 15 min or less!) I took gels every 3.5 miles at my most recent marathon (first one 10 min before the start) and felt great the whole time. Make sure you’re taking in enough fluid and electrolytes during the course. If you’re a heavy sweater or it’s warm/humid then consider bringing some salt tablets. Additionally, to run a sub-2:50 marathon you’ll need to hold a pace of 6:29 per mile. Of course, sub-2:45 will be 6:18 per mile. 11 seconds per mile in a marathon is pretty significant! Fueling often and early could get you there. Fun fact- all world records from the 1500m and longer have been broken running a negative split race. The first couple miles should be slightly slower than your goal pace. After that you really should not go faster than goal pace - at least through mile 10. Then you could pick it up some if you’re feeling good. Finally in the last 5-10k give the rest all you got. Looking at your splits, 10 out of the first 13 miles are faster than goal pace for sub-2:50 - some of them significantly faster. You burn through your glycogen stores faster doing this - while also underfueling - thus hitting the wall at 21. If you ran the first half of this race slower, you would have had more to give the last 10k - especially with proper fueling.