help me please!

On monday my car was totaled by some lady who ran a red a red light. She was issued a citation by the police. I was taken to the hospital and given two X-rays but was ok. I still had some severe pain. The next day some insurance guy came to my house and offered me $1000 on the spot. I know nothing about the law, so me being a broke college student accepted the offer after he told me that this was the common procedure. Now I am told I could have sued and got at least $5000. I want to know is it too late to pursue a case because I already recieved $1000 and signed the paperwork???