Job Update.... Is it too late to panic?

I have just spent the entire day fretting about the job I accepted yesterday.
I'm very worried that the role of ICT technician isn't one I can actually do.

Bit of background first.
The job is advertised as an ICT technician in a primary school of 200 pupils, roughly 30 computers, all networked and Internet linked.
But from the job description and from what I gathered at interview they want someone capable of engaging with the pupils and essentially being an ICT Teaching Assistant. This is great. It's just the sort of thing I wanted to do and I'm really looking forward to that part of the job.
But they also want someone to keep the network working.
The ICT technician that's off on maternity leave for the duration of the job Jan -July has set the network up and everything sounds like it's running okay.

BUT....
I'm panicking because I have so very little knowledge of networks it's scary.
Never needed to know about them, never bothered to learn.
But I just know that I'm not going to get away with 7 months of not doing anything with the network. And I'm a touch concerned that it just won't be good enough to learn on the job with this one. There's no-one on site I can ask for help with this. And this concerns me. I hate the idea of starting there and having it all go wrong with no-one to turn to for help.

So it's worry, worry, worry.
Hasn't helped that I seemed to spend today on the phone failing to get a bloody course on networking sorted.

Tomorrow I'm popping along to the school to hand in p45s and talk about things. Probably not the best idea to mention this yet. Maybe I should wait until I actually start the job?