I totally empathise with you, because I've had to deal with insurance companies before, and I know what it's like to be short on cash and having to deal with other debts, other commitments etc. Yes, you may end up being screwed, but before you sign anything, before you accept any settlements, look into the options the others have mentioned, such as getting legal advice, and going to the small claims court to sue the idiot who totalled your car. And make sure the insurance company doesn't try to intimidate you into anything!!!
Sorry that you are in this situation. It sucks, but it does leave you more informed for the next time you insure a car. Sometimes life teaches us lessons the hard way.