Should I negotiate my severance?, warehouse supervisor here

I was offered 12 weeks of severance after 12 years as a warehouse supervisor, 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. Should I see a lawyer?

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

Ask for the offer in writing and do not sign on the spot. A day or two to think is normal.