What to do when seeing ex boyfriend for first time since breakup

M
I haven't seen my ex since we broke up a couple of months ago. I'm going on Wednesday to pick up the stuff I left at his apartment and give him back a tshirt. I go back and forth between feeling totally over him and kind of missing him. I know that it's totally over but I'm kind of nervous about seeing him again. The breakup was pretty mutual and we said we wanted to stay friends, but we might have just said that because that's what you're supposed to say sometimes haha. Do you have any words of encouragement? They would be very appreciated in my hour of need! How can I get through Wednesday?