Should I negotiate my severance? after 4 years as an IT help-desk technician

My manager said the package is final, but the letter gives me time to review. This is my first time dealing with any of this. There is a non-disparagement clause.

An hour with an employment lawyer cost me a small fee and made me feel much safer about signing.

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