grandma's looks annual and open entry. there will be a 25 race. a 26 race. a 27 race. and so on. you can always do the next. college you get one run through. you either want to run that last year of college or not. this isn't boston or NY, there isn't a qualifying or lottery between you and doing this ever again. you finish college, you do 26 or so. it will be there waiting. that is, if you want. maybe you're over it. then shift to adult reality. and be sure you won't regret it.
anyhow, to me this post is a walking "sunk costs fallacy." but i met this coach. but i entered this race. but i have sunk costs on doing this new thing. so? you can tell the coach you will be back in x months to re-start. you can enter the next race.
what is it you want to do now?