Work help?

This is for someone who works or really anyone who has advice .. I started a job at McDonald’s , except I’m still “in training” I guess but next Sunday is my sweet 16 and this was already planned before I got my job, so if I work that day I’m gonna be nervous asking for that day off ... when I’m not even a worker yet.. and I don’t want to feel like I’m blowing it off or making the managers feel I’m not right for the job because I can’t work one day ,, someone please help with advice 😂😫