From what I have heard, getting into CSULB is one of the more difficult. This is due to it being considered one of the better programs, and it being significantly less expensive. I have seen many people on these forums choose CSULB over USC for the very reason of the price difference. I know of quite a few people with similar stats to you who have been accepted to USC so I think you have a decent to good chance of getting in. I would say your chances to get into CSUF and CSUN are good.
For a long time I thought that USC was going to be the school I would go to for my MSW, but after a lot of research and talking to people in the SW field, I decided it wasn't worth the cost so I didn't even apply. When it comes to SW it is a bit different from other graduate programs. It doesn't really matter all that much which school you go to and how much prestige the school has. This is different than say going to law school. What about USC makes it your dream school?
If you really think USC is the school for you, you have to make a plan. Determine how much total tuition, books, and materials will be and how much you will need for living expenses. If it is going to require taking out a loan, determine how much you will be paying monthly and for how long. Be sure to take into consideration where you plan to live once school is done and how much you will realistically be making as a SW. I've read that a monthly loan payment should never be more than 15% of your monthly income. If it's more than that, it can really impact the lifestyle you live once you are done with school.
Going to your dream school would be amazing, but you have to consider how it will effect things once you are out of school. I know many people who have gone to their dream school and taken on an insane amount of debt to do it. For many of them it's a decision they regret, while others think it was totally worth it and they would do it again in a heartbeat. You just need to make sure you look at everything and are ok with your choice.