Should I negotiate my severance?, copywriter here

I was offered 3 weeks of severance after 3 years as a copywriter, and I have a few days to sign. I would rather hear the honest version than the polite one. I do not want to leave money on the table. Did anyone negotiate and succeed?

Thanks for writing this out. I went through something close to it 8 months ago, and it got easier once I kept a simple log of every call and form.