Can I get written up or fired?

I feel that you did what you had to do to get the day covered. You left messages and they never returned your call. If they say anything to you when you go back to work, just explain that the new manager did not look at your availability and scheduled you for days you are not available. If they needed you for the weekend, he should asked you if you could work this weekend. This is the new managers fault, Not yours. Then ask this new manager to check availability before scheduling people. Good Luck