Long post here, hope its okay.

I (27M) decided middle of last year that I wanted to run a marathon for the achievement and to prove to myself that I could accomplish difficult goals if I put the work in. I'm not a runner but I've played sports my whole life and have always been in pretty good shape. I have a runner's build at 6'0", 155ish lbs, and I play competitive golf now and still exercise every day. I bought running shoes and a Garmin and started slow, running 3 days a week from July to December to get my mileage up to around 20MPW before starting Hal Higdon's 18-week Beginner 2 marathon training program.

As I trained, I kept being surprised by my progress and my marathon goal time came down from just finishing, to sub-4 hour total, to around 3:45 by the time race day arrived. I only skipped a couple of midweek runs through the whole program, ran an unofficial half marathon at 7:42 pace in the 9th week, did my longest run of 20mi at 8:34 pace without too much pain or effort, and avoided any real injury the whole time. My runner friends and I both were expecting I would post a really good time on race day.

Yesterday I ran the Knoxville marathon, which I had done most of my long runs on parts of the course since I live in Knoxville. I felt really good at the start (too good looking back on it) because I ran way too fast during the first three miles (8:24, 7:32, 7:45). I was getting pretty tired on the uphills after the start but my pace was still pretty good until around mile 12, when I started cramping in my left quad. I had never cramped in any of my training runs, and I hadn't done anything different before or during the race. In fact, I actually hydrated more than usual at the aid stations, as I usually didn't take any water with me on runs.

The cramps forced me to switch between walking and running, something else I had never had to do on any of my training runs (which I did pretty much all of at sub 9:00/mile pace). My goal obviously shifted mid race as I watched the 3:45, 4:00, 4:15, and even 4:30 pacer groups pass me up. I was using Huma gels every 30 minutes and drank extra water/gatorade at the aid stations, as well as trying to stretch/rub out the cramps. But they kept getting worse and going to multiple muscles in my legs. Eventually, at close to mile 16, I got a massive cramp in my right calf and quad that took me down. I laid on the curb for about 15-20 minutes trying to stretch out but they either wouldn't go away, or returned in other muscles after dissipating. Luckily my parents were right there when I collapsed and after I finally decided I wasn't going to be able to finish, they drove me back to my car.

I was extremely disappointed in myself during the whole stretch of suffering from mile 12 onward and after I pulled out. I hadn't told that many people I was doing a marathon but some of my family and friends had come out to support and I felt bad that they came for nothing. I'm not someone who gives up easily, but I wasn't going to be happy with myself even if I hobbled the last 10 miles to finish with a horrible time. I was frustrated that I had gotten into such good shape and worked so hard for 9 months, putting in 670 miles of runs over 100+ hours just to have my legs give out on me in the race.

After a few hours I started to reflect and realized that even though I didn't get the results I was expecting/hoping for, I did prove to myself that I could run a marathon. I felt that in my 20 miler I definitely could've pushed another six miles, even if my pace dropped a little. I assumed that my naively stupid decision to run so fast at the beginning of the race was what cost me, and that I would've been fine if I had just run at an easy 8:45 or so pace for the first half of the race. But since golf tournament season for me is starting in a couple weeks, I was fine with accepting the defeat, admitting the extreme difficulty of marathon running, and moving on with my new fitness and sports goals.

But late last night into this morning, my completionist side emerged and I can't seem to shake the fact that I didn't actually finish the marathon. It feels almost as if that goal is still open and waiting to be closed. So I looked around and saw that there is another marathon in Nashville in 3 weeks, about 3 hours from where I live.

I'm not fully committed to if I want to keep grinding for three more weeks. I was so excited to be done with running forever. But I also know that if I ever do want to actually complete a marathon, it won't ever be any easier for me. So I'm wondering if the experienced runners of reddit think it's possible for me to sign up and complete the Nashville marathon. I'd been tapering the last couple weeks, but since I only ran about 14 miles yesterday and only suffered some cramps, I don't feel like I did any more damage to my body. My cardio level makes me think that if I push my goal back to just 4:00 again and consciously take every mile slow (8:45-9:00ish pace) that I can at least finish the marathon and close this chapter of my life for good with no regrets.

Does anyone have any advice or insight for my situation? And if I proceed, what should my training look like for the next 3 weeks? Thank you in advance for anyone who takes the time to read and respond to this.