You’re in denial if you don’t know what to improve. Hopefully you’ll be laid-off instead of fired. Although, if you’re a short term employee with a lower title, the “standard” resign-so-we-don’t-have-to-fire-you package (3 months pay & insurance) might be better than a lay-off package. You might negotiate that to four months.
Being on a PIP and not knowing what to improve is not a good sign. If you were actually motivated, you would be asking your supervisor others around you for advice on how to improve. Your review is generally based on the feedback from those who work directly with you. Apparently they aren’t too impressed with your work.