You'll be absolutely fine, I would say it's easier than a half IMO. The Hell part of hell-runner is bit over-rated, it's just a fun jaunt on a Autumnal day, up and down a few hill and through a few water features. I guess it depends partly on the weather, and how seriously you take it though.
I enjoyed the run, however the most hellish part of it was the worst, most disorganised baggage tent I've ever seen, I would avoid using that at all costs. Oh and you might want to check double check the start times, last year they confusingly displayed two different start times for the one wave on their website, so some people started well after the rest of the field, genius .... organisation in the past has not been a strong point of hellrunner.
I see this year they're having two waves which might make it a little less congestested, assuming they haven't just doubled the number of runners.
With 10 weeks still to go you've got plenty of time to get in a bit of training off-road, and a few hill sessions, it will be a breeze! Enjoy!