Welcome to the forums :)
Looks to me like you are doing extremely well. Are you claiming all child tax credits and transit credits and such that you may be entitled to?
If you pay off your SL and maintain that 60% Savings rate, plus any income increases, you'll be in excellent shape!
For suggestions, I would just suggest that you look into free family activities so you can keep up that high savings rate while still having fun.
You might be able to whittle a bit off your grocery budget, but depending where in CA you are and with working a full-time job and being a single mom it might not be worth it to pinch the pennies instead of spending time with your kid.