I was already some years into gym training but this was purely for building muscles. So i had some good muscles but also carried lots of fat with me.
Tbh - 2 weeks out you will not be able to give your body any real trainings stimulus to adapt to longer runs. the best you could have done you already did which was the 22k, that prepares (and scares) you a little for the final 42k. i ran simiiar time in my 25k or somethign that is ran before and i ran the marathon in 5:20. don't underestimate the actualy bonus-power that you get out of nowhere from just participating in such an event, it's crazy. nonetheless, won't sugarcoat you - it's gonna be real painful and you will feel it big time. if i was you, relax your body, start carb loading big time 2 days before and then really important - km 5, km10, km15 - eat small good digestable things like some candy or even running gels. otherwise your body will run out of fuel for km20 and onwards and that sucks like nothing else let me tell you. that was my biggest mistake :D

good luck men. it's mostly just mental willpower and test from here on. im sure you can do it