Severance agreement arrived, need a second opinion, production planner here

I was offered 3 weeks of severance after 3 years as a production planner, and I have a few days to sign. I am in Pittsburgh, in case local advice matters. 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.

Keep everything in writing and save the confirmation numbers. It saved me later.