If you are at an allopathic school, then you DEFINITELY can improve your app to match in So Cal. I have a couple friends who went through the whole application process for peds last year, and one of them had less than a 215 on the STEP 1. She had other good things on her app however, and was interviewed at some very competitive programs, including Northwestern, Texas Childrens' and Rainbow Babies.
So Cal has a wide variation in competitiveness for programs. The only two that I would say are extremely difficult are UCLA and CHLA. Harbor-UCLA and CHOC are slightly less competitive. Also, USC has its own program separate from CHLA, which I've heard is not difficult to match into at all, at least relative to CHLA.
Just do as well as you can on STEP 2, honor your Peds core rotation, and maybe think about setting up an away elective at a program in So Cal. Also, talk to your school's peds chairman about what else you can do to improve.