First of all... thank you
Second of all...
It doesn't really matter what is a person focused at. I will edit the original post after this so if someone is reading this after that, don't be confused.
Thanks for reminding...
Anyway the point is that we all do level design to a degree.
You simply choose a map from the story-line that you like the best and you work at it.
If someone is already working on that map, you join him/her.
If you have a problem with a script that's not working, you mark it as Bugged and continue on your other work.
If you're scripting you can just go and fix bugs or you can review finished maps and fix little bugs.
You basically do the work you're good at or the work you want to be good at.
If you want to get better at scripts, you simply team up with the person that does scripts and he can perhaps give you a little tour through his .hps files...
There are no strict rules. It's a hobby, it takes time. It should be fun... Anything is possible if you just ask. =)