despite the fact that you are a competitive runner and very time/goal oriented, for your first mara you def should just focus on finishing and enjoying the race. if you do those 2 things, your finish time will be really good still just bc you will be very well prepared. but if you are gunning for 2:45 and fall apart at mile 18 as a result, you may not finish or you may crawl in at 3:30. truth.
i think you will be fine, just ramp up your long runs sort of quickly. the LR is the key part of marathon training, IMO. if you want to hit, say, 80 mpw and you include 2 10mi junk runs early in the week, maybe notch those down to 8mi that way your legs have the LR in them for the end of the week.
also, working tempo miles into LRs is a really good way to increase endurance beyond just time on your feet. (for example, if you're doing a 18mi run, maybe do 10mi easy, 4mi @ 13.1mi pace, 4mi @ 10k pace)
counting back from race day...
0 weeks: 26.2
1 week: 10 please read about how to taper. this is important.
2 week: 22
3 week: 21
4 week: 20
5 week: 13 and dial your workouts back this week also
6 week: 19
7 week: 17.5
8 week: 16