This one is going to sound too simple to mention. Body language matters. Practice your scenario again today and this time sit up straight and keep your hands out in the open and relaxed.
Here is a quick reminder of where we are in the process of preparing to negotiate:
Day 1 - Know your contribution to the company.
Day 2 - Know the values of the other person. (In this case, your boss)
Day 3 - Understand the company policy regarding flexible schedules.
Day 4 - Know how you are perceived.
Day 5 - Sketch out a scenario to practice and find a practice partner.
Day 6 - Practice the scenario you sketched out. Ask yourself if you were balanced in your approach. Were you realistic but not apologetic or boastful?
We are getting close to the end of the process! I can see it now, you will be so calm, focused and professional when you negotiate because you have put the time into improving a skill.