Severance agreement arrived, need a second opinion - first time posting

I was offered 12 weeks of severance after 12 years as a sales associate, and I have a few days to sign. I have read a lot of threads here and could not find my exact situation. I do not want to leave money on the table. Did anyone negotiate and succeed?

I asked for two more weeks and a neutral reference. They agreed to the reference and added a week.